Q.Find the equation of the hyperbola with eccentricity 23 and foci at (±2,0).
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Hyperbola
The standard hyperbola a2x2−b2y2=1 has centre at the origin,
transverse axis 2a, conjugate axis 2b, and eccentricity e with
b2=a2(e2−1), so e>1. Its foci are (±ae,0), directrices x=±ea, and
each latus rectum has length a2b2; the asymptotes are y=±abx.
The conjugate hyperbola is a2x2−b2y2=−1, whose eccentricity
e′ satisfies e21+e′21=1.
The line y=mx+c touches the hyperbola iff c2=a2m2−b2, giving the tangent
y=mx±a2m2−b2; the tangent at (asecθ,btanθ) is
axsecθ−bytanθ=1. A general hyperbola is put in this
form by completing squares (translation of centre) or by a rotation. These tools …
The key idea is understanding the Standard Form of a Hyperbola and the relationships between its parameters (a,b,c,e).
- The foci are given as (±2,0). This indicates the hyperbola is centered at the origin (0,0) and its transverse axis lies along the x-axis. From the foci, we have c=2.
- The eccentricity is given as e=23. For a hyperbola, e=ac. Substituting the values, we get 23=a2, which implies 3a=4, so a=34.
- For a hyperbola, the relationship between a,b,c is c2=a2+b2. Substituting c=2 and a=34: 22=(34)2+b2 4=916+b2 b2=4−916=936−16=920. …
We determine the hyperbola's orientation and parameters (a2 and b2) from the given foci and eccentricity, then substitute these into the standard equation to get 169x2−209y2=1.
To find the equation of a hyperbola, we need to determine its orientation (whether the transverse axis is horizontal or vertical) and the values of its key parameters, a2 and b2. The given information — the foci and eccentricity — directly helps us find these.
The standard form of a hyperbola centered at the origin depends on where its foci lie.
- If the foci are on the x-axis at (±c,0), the transverse axis is horizontal, and the equation is a2x2−b2y2=1.
- If the foci are on the y-axis at (0,±c), the transverse axis is vertical, and the equation is a2y2−b2x2=1.
The eccentricity e of a hyperbola is defined as the ratio e=ac, where c is the distance from the center to a focus, and a is the distance from the center to a vertex. For a hyperbola, e>1.
The relationship between a,b,c for a hyperbola is c2=a2+b2. This can also be expressed as b2=a2(e2−1).
Let's apply these concepts to the given problem.
- Identify the type of hyperbola and its center: The foci are given as (±2,0). Since the y-coordinate is zero, the foci lie on the x-axis. This means the transverse axis of the hyperbola is along the x-axis, and the hyperbola is centered at the origin (0,0). Therefore, the standard form of its equation will be:
a2x2−b2y2=1
-
Determine the value of c:
The foci are at (±c,0). Comparing this with the given foci (±2,0), we find that c=2.
-
Determine the value of a using eccentricity:
We are given the eccentricity e=23.
The definition of eccentricity for a hyperbola is e=ac.
Substitute the known values of e and c:
23=a2
Now, solve for $a$:
3a=2×2
3a=4
a=34
Then, $a^2 = \left(\frac{4}{3}\right)^2 = \frac{16}{9}$.
4. Determine the value of b2:
We can use the relationship b2=a2(e2−1). This is often more direct when eccentricity is given.
Substitute the values of a2 and e: …
Showing the 12 most recent of 69 on this concept.
- AP EAPCET 2026Set eng-2026-05-12-FN1 markMCQQ.Let X-axis be the transverse axis and origin be the centre of a hyperbola. If its latus rectum subtends an angle of 150∘ at its vertex, then its eccentricity is (A) 3+1 (B) 2+3 (C) 1+2 (D) 2+2
›Reveal solutionSolution
Half the subtended angle gives tan(θ/2)=e+1 for a hyperbola's latus rectum viewed from its vertex; solving with θ=150∘ gives e=3+1.
Concept and Intuition
The latus rectum through a focus (ae,0) has endpoints (ae,±b2/a). Viewed from the nearer vertex (a,0), symmetry about the X-axis means the full subtended angle is twice the angle to one endpoint, and this angle simplifies neatly in terms of the eccentricity alone.
Step-by-Step Solution
- Hyperbola a2x2−b2y2=1, vertex (a,0), right focus (ae,0), latus rectum endpoints (ae,±b2/a).
- Half-angle at vertex to one endpoint: tan(75∘)=ae−ab2/a=a2(e−1)b2.
- Using b2=a2(e2−1): tan75∘=a2(e−1)a2(e2−1)=e−1(e−1)(e+1)=e+1.
- tan75∘=tan(45∘+30∘)=2+3 (standard value). …
- AP EAPCET 2026Set eng-2026-05-12-AN1 markMCQQ.Let S, S' be the foci of a standard hyperbola a2x2−b2y2=1 and its eccentricity be 5. If 'b' is the radius of a circle concentric with the hyperbola, then the number of points of intersection of the circle and the hyperbola is (A) 4 (B) 2 (C) 0 (D) 1
›Reveal solutionSolution
The circle of radius b=2a concentric with the hyperbola a2x2−b2y2=1 (with e=5) intersects it at exactly 4 real points.
Concept and Intuition
For a hyperbola, b2=a2(e2−1). Here e=5 gives b2=4a2, i.e. the circle's radius b=2a is bigger than the hyperbola's vertex distance a, so we expect the circle to genuinely cross both branches — the question is exactly how many points that produces.
Step-by-Step Solution
- b2=a2(e2−1)=a2(5−1)=4a2, so radius of circle =b=2a, circle: x2+y2=4a2.
- From the hyperbola: x2=a2(1+b2y2)=a2+4a2a2y2=a2+4y2.
- Substitute into the circle: a2+4y2+y2=4a2⇒45y2=3a2⇒y2=512a2.
- This is positive, giving two real values y=±512a2.
- Then x2=a2+41⋅512a2=a2+53a2=58a2, also positive, giving x=±58a2. …
- AP EAPCET 2026Set eng-2026-05-13-FN1 markMCQQ.The equation of the conjugate hyperbola of the hyperbola x2−4y2−2x−8y−19=0 is (A) x2−4y2−2x−8y−33=0 (B) x2−4y2−2x−8y+33=0 (C) x2−4y2−2x−8y+13=0 (D) x2−4y2−2x−8y−13=0
›Reveal solutionSolution
Completing the square gives the hyperbola (x−1)2−4(y+1)2=16; its conjugate flips the sign of the right side to −16, expanding to x2−4y2−2x−8y+13=0.
Concept and Intuition
For a hyperbola a2X2−b2Y2=1, the conjugate hyperbola is b2Y2−a2X2=1 — equivalently, keep the same quadratic/linear terms but negate the constant on the right (or, in the "=k" form, replace k by −k), about the same centre.
Step-by-Step Solution
- Group and complete the square: x2−2x−4(y2+2y)−19=0⇒(x−1)2−1−4[(y+1)2−1]−19=0.
- ⇒(x−1)2−1−4(y+1)2+4−19=0⇒(x−1)2−4(y+1)2−16=0⇒(x−1)2−4(y+1)2=16.
- This is 16(x−1)2−4(y+1)2=1 — centre (1,−1), a2=16,b2=4.
- The conjugate hyperbola replaces 16 by −16: (x−1)2−4(y+1)2=−16, i.e. (x−1)2−4(y+1)2+16=0. …
- AP EAPCET 2026Set eng-2026-05-14-AN1 markMCQQ.From a point P(x1,−1) (x1<0), two tangents are drawn to the hyperbola 2x2−3y2=1. If the sum of the slopes of the tangents is 2, then x1= (A) −1 (B) −2 (C) −31 (D) −52
›Reveal solutionSolution
Writing the tangent-line quadratic in slope m for tangents from P(x1,−1) to the hyperbola, and using "sum of roots =2" as the given condition, yields x1=−2.
Concept and Intuition
From an external point, exactly two tangent lines touch a conic; their slopes are the two roots of a quadratic obtained by substituting the tangency condition into the fact that the line passes through the point. Vieta's formulas then let us use "sum of slopes" or "product of slopes" as an equation in the point's coordinates — we never need to find the individual tangent lines.
Step-by-Step Solution
- For 2x2−3y2=1 (a2=2,b2=3), a line y=mx+c is tangent iff c2=a2m2−b2=2m2−3.
- The tangent passes through P(x1,−1): −1=mx1+c⇒c=−1−mx1.
- Substitute: (−1−mx1)2=2m2−3.
- Expand: 1+2mx1+m2x12=2m2−3.
- Rearrange: m2(x12−2)+2x1m+4=0.
- This quadratic's two roots are the slopes m1,m2 of the two tangents. By Vieta, m1+m2=x12−2−2x1. …
- AP EAPCET 2026Set eng-2026-05-13-AN1 markMCQQ.If the tangent and normal at any point on the hyperbola x2−y2=a2 cut off intercepts a1 and a2 on X-axis, b1 and b2 on Y-axis respectively, then (A) a1a2=b1b2 (B) a1b2=a2b1 (C) a1b2+a2b1=0 (D) a1a2+b1b2=0
›Reveal solutionSolution
Relates the axis-intercepts of the tangent and normal to a rectangular hyperbola; the identity is a1a2+b1b2=0.
Concept and Intuition
On a rectangular hyperbola x2−y2=a2, the tangent and normal at a point have slopes that are negative reciprocals of each other's coordinate ratio in a special way, which forces a clean symmetric relation between their intercepts.
Step-by-Step Solution
- Let the point be (x1,y1) with x12−y12=a2.
- Tangent: differentiating implicitly, 2x−2yy′=0⇒y′=x/y, so tangent slope at the point is x1/y1. Tangent: xx1−yy1=a2.
- x-intercept a1 (set y=0): a1=a2/x1.
- y-intercept b1 (set x=0): b1=−a2/y1.
- Normal: slope =−y1/x1 (negative reciprocal). Line: y−y1=−x1y1(x−x1).
- x-intercept a2 (set y=0): −y1=−x1y1(x−x1)⇒x−x1=x1⇒a2=2x1. …
- AP EAPCET 2026Set eng-2026-05-15-AN1 markMCQQ.Consider the Hyperbola S≡25x2−16y2−1=0. Let B,B′ be the ends of the transverse axis of the conjugate hyperbola of S=0. If C is the circle with B,B′ as ends of diameter, then slope of a common tangent to C and the given Hyperbola is (A) ±432 (B) ±342 (C) ±453 (D) ±233
›Reveal solutionSolution
This tests tangent-line conditions to a hyperbola and a circle simultaneously. Identifying the conjugate hyperbola's transverse-axis circle and equating both tangent-constant formulas gives the common slope.
Concept and Intuition
The conjugate of a2x2−b2y2=1 is b2y2−a2x2=1, whose transverse axis lies along the y-axis with half-length b. A common tangent to two curves must have the same slope-form equation for both, so equating the two tangent-condition expressions in m solves for the shared slope.
Step-by-Step Solution
- For S:25x2−16y2=1, a2=25,b2=16.
- Conjugate hyperbola: 16y2−25x2=1; its transverse axis is along the y-axis with half-length 16=4, so B=(0,4),B′=(0,−4).
- Circle C on diameter BB′: centre origin, radius 4, i.e. x2+y2=16.
- Tangent of slope m to S: y=mx±25m2−16.
- Tangent of slope m to C: y=mx±41+m2. …
- AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQQ.If d1 and d2 are the distances of the foci of the hyperbola 4x2−9y2−16x+54y−101=0 from the point (2 , −3), then d1+d2= (A) 10 (B) 14 (C) 12 (D) 16
›Reveal solutionSolution
This tests reducing a hyperbola to standard form and then computing plain distances from a given point to its two foci; the sum is 14.
Concept and Intuition
The point (2,−3) is not on the hyperbola, so the constant-difference-of-distances property does not apply here — we simply need the ordinary distance from a point to each focus and then add them.
Step-by-Step Solution
- Group and complete the square: 4x2−16x−9y2+54y−101=0 ⇒4(x2−4x+4)−16−9(y2−6y+9)+81−101=0 ⇒4(x−2)2−9(y−3)2−36=0⇒4(x−2)2−9(y−3)2=36.
- Divide by 36: 9(x−2)2−4(y−3)2=1. Centre (2,3), a2=9,b2=4.
- c2=a2+b2=13⇒c=13. Foci: (2+13,3) and (2−13,3). …
- AP EAPCET 2026Set eng-2026-05-18-FN1 markMCQQ.If C is the centre of the hyperbola a2x2−b2y2=1 and the tangent drawn at any point P on the hyperbola meets the lines bx−ay=0 and bx+ay=0 at Q and R respectively, then CQ⋅CR= (A) a2−b2 (B) a2+b2 (C) a21+b21 (D) a21−b21
›Reveal solutionSolution
Parametrising the hyperbola and intersecting its tangent with the two asymptotes gives
CQ⋅CR=a2+b2, independent of the point P chosen — a clean invariant.
Concept and Intuition
The lines bx∓ay=0 are exactly the asymptotes of the hyperbola a2x2−b2y2=1.
A well-known property is that the tangent at any point of a hyperbola cuts its two asymptotes in
points whose distances from the centre multiply to the constant a2+b2 — this is analogous to
(and provable the same way as) the "tangent cuts a constant area triangle with the asymptotes"
property.
Step-by-Step Solution
- Let P=(asecθ,btanθ). The tangent at P is
axsecθ−bytanθ=1
- Intersect with y=abx (i.e. bx−ay=0):
axsecθ−btanθ⋅abx=1⇒ax(secθ−tanθ)=1⇒x=secθ−tanθa
Then y=secθ−tanθb, so
CQ=x2+y2=∣secθ−tanθ∣a2+b2
- Intersect with y=−abx (i.e. bx+ay=0) similarly: …
- AP EAPCET 2026Set eng-2026-05-18-AN1 markMCQQ.A normal is drawn to the hyperbola 9x2−16y2=144 at one of the ends of its latus rectum. If that end lies in the third quadrant and the equation of the normal is ax+by+c=0, then ab+c= (A) 2544 (B) 2584 (C) 1655 (D) 16145
›Reveal solutionSolution
This tests locating the latus-rectum endpoints of a hyperbola in the correct quadrant and applying the standard normal-line formula at that point. The normal's coefficients give ab+c=16145.
Concept and Intuition
For a2x2−b2y2=1, the foci are at (±c,0) with c2=a2+b2, and the latus rectum through each focus has half-length b2/a, so its ends are (±c,±ab2) (four combinations, one per quadrant containing a focus). The normal at a point (x1,y1) on the hyperbola is obtained by differentiating implicitly to get the tangent slope, then taking the negative reciprocal for the normal slope — this simplifies to the clean symmetric form x1a2x+y1b2y=a2+b2, analogous to the ellipse's normal formula.
Step-by-Step Solution
- 9x2−16y2=144. Divide by 144: 16x2−9y2=1. So a2=16 (a=4), b2=9 (b=3), c2=a2+b2=25 (c=5).
- Latus-rectum ends: (±c,±ab2)=(±5,±49).
- The end in the third quadrant (both coordinates negative) is (−5,−49).
- Normal to the hyperbola at (x1,y1): x1a2x+y1b2y=a2+b2. With a2=16,b2=9,x1=−5,y1=−49:
−516x+−9/49y=16+9=25.
- Simplify −9/49y=9y⋅(−94)=−4y. So:
−516x−4y=25.
- Multiply through by −5: 16x+20y=−125⇒16x+20y+125=0.
- This matches the form ax+by+c=0 with a=16,b=20,c=125. …
- AP EAPCET 2025Set eng-2025-05-21-FN1 markMCQQ.One of the latus recta of the hyperbola a2x2−b2y2=1 subtends an angle 2Tan−1(23) at the centre of the hyperbola. If b2=36 and e is the eccentricity of the given hyperbola, then a2+e2= (A) 4 (B) 14 (C) 6 (D) 21
›Reveal solutionSolution
Using the latus-rectum-subtended-angle formula tanθ=a2eb2 together with the eccentricity relation e2=1+a2b2, solve for a2 and e, then compute a2+e2.
Concept and Intuition
A latus rectum of the hyperbola a2x2−b2y2=1 passes through a focus (±ae,0) and has half-length ab2, so its two endpoints are (ae, b2/a) and (ae, −b2/a). From the centre (origin), each endpoint subtends a half-angle θ with tanθ=aeb2/a, so the full angle between the two lines from the centre to the endpoints is 2θ. Combined with the standard hyperbola relation b2=a2(e2−1), this gives enough equations to solve for a2 and e.
Step-by-Step Solution
- Latus rectum endpoints: (ae,b2/a) and (ae,−b2/a). Half-angle at centre: tanθ=aeb2/a=a2eb2.
- Given full angle =2tan−1(3/2), so θ=tan−1(3/2)⇒tanθ=23.
- So a2eb2=23. With b2=36: a2e36=23⇒a2e=24.
- Eccentricity relation: e2=1+a2b2=1+a236.
- Let A=a2. From step 3, e=A24, so e2=A2576. Substitute into step 4: A2576=1+A36 ⇒ 576=A2+36A ⇒ A2+36A−576=0. …
- AP EAPCET 2025Set eng-2025-05-21-FN1 markMCQQ.If the equation of the hyperbola having (8, 3), (0, 3) as foci and 34 as eccentricity is p(x−α)2−q(y−β)2=1 then p+q= (A) β2 (B) α+β (C) α2 (D) αβ
›Reveal solutionSolution
The centre of the hyperbola is the midpoint of its foci, giving α=4,β=3; using c=4 and e=4/3 we find a2=9, b2=7, so p+q=16, which equals α2.
Concept and Intuition
A hyperbola centred away from the origin, p(x−α)2−q(y−β)2=1, has its centre (α,β) at the midpoint of its two foci, and its focal parameters c (half the distance between foci), a=p (semi-transverse axis) and b=q (semi-conjugate axis) obey b2=c2−a2 and e=c/a, exactly as for a hyperbola centred at the origin — just shifted.
Step-by-Step Solution
- Foci: (8,3) and (0,3) — same y-coordinate, so the transverse axis is horizontal, and the centre is their midpoint: (α,β)=(28+0,3)=(4,3).
- Distance between foci =2c=8⇒c=4.
- Eccentricity e=34=ac⇒a=ec=4/34=3⇒p=a2=9.
- b2=c2−a2=16−9=7⇒q=7.
- p+q=9+7=16. …
- AP EAPCET 2025Set eng-2025-05-22-AN1 markMCQQ.If the equation of the tangent of the hyperbola 5x2−9y2−20x−18y−34=0 which makes an angle 45° with the positive X-axis in positive direction is x+by+c=0 then b2+c2= (A) 2 or 13 (B) 5 or 26 (C) 2 or 26 (D) 26 or 28
›Reveal solutionSolution
This tests the tangent condition for a hyperbola with given slope, after recentring by completing the square. The answer is b2+c2=2 or 26.
Concept and Intuition
Any conic given by a general second-degree equation with no xy term can be recentred by completing the square in x and y separately. Once in standard form a2X2−b2Y2=1, the classical tangent condition (line Y=mX+c touches the hyperbola iff c2=a2m2−b2) applies directly in the shifted coordinates.
Step-by-Step Solution
- Complete the square:
5x2−20x=5(x−2)2−20,−9y2−18y=−9(y+1)2+9
So the equation becomes 5(x−2)2−9(y+1)2−45=0, i.e.
9(x−2)2−5(y+1)2=1
Here a2=9, b2=5, and shifted coordinates are X=x−2, Y=y+1.
-
A line making 45° with the positive X-axis has slope m=tan45°=1.
-
Tangent condition for Y=mX+c to touch a2X2−b2Y2=1:
c2=a2m2−b2=9(1)2−5=4⟹c=±2
- Convert back to x,y: Y=X+c⇒(y+1)=(x−2)+c⇒x−y+(c−3)=0.
Matching to the given form x+by+c=0 (calling the constant c′ to avoid clash with the value above): b=−1, and …
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