Q.Compute the area bounded by the lines x+2y=2, y−x=1 and 2x+y=7.
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Area Under a Curve
How do you measure the area of a region whose top edge is curved rather than a straight line? For rectangles and triangles we have formulas, but a shape bounded above by y=f(x) has no simple side lengths to plug in. The definite integral is the tool built exactly for this.
The core idea: area as a limit of strips
Take the region under y=f(x) (with f(x)≥0), above the x-axis, between x=a and x=b. Slice it into many thin vertical strips. A strip at position x with tiny width dx is almost a rectangle of height f(x), so its area is about f(x)dx. Add up all the strips and let their width shrink to zero: the sum becomes the definite integral
Area=∫abf(x)dx.
This is why the integral is the area — it is the exact total of infinitely many infinitesimally thin rectangles.
How to compute it
Find an antiderivative F(x) (so F′(x)=f(x)) and evaluate at the two limits — the Fundamental Theorem of Calculus:
∫abf(x)dx=F(b)−F(a).
For example, the area under y=x2 from 0 to 1 is [3x3]01=31.
Cases you must handle carefully
The integral gives signed area. Where the curve dips below the x-axis, f(x)<0 and ∫fdx comes out negative. For the geometric (positive) area of such a stretch, integrate the absolute value or take the magnitude of that piece: Area=∫ab∣f(x)∣dx.
If a curve crosses the x-axis inside [a,b], split the integral at each crossing and add the sizes of the parts.
Area with respect to the y-axis
When the region is bounded by a curve x=g(y) and the y-axis between y=c and y=d, slice horizontally instead: …
Concept: Area Under Curve — the region is a triangle formed by three intersecting lines.
Step 1 – Find intersection points
Solve pairwise:
- x+2y=2 and y−x=1: adding gives 3y=3⇒y=1, then x=0. Point A(0,1).
- y−x=1 and 2x+y=7: subtract first from second: (2x+y)−(y−x)=7−1⇒3x=6⇒x=2, then y=3. Point B(2,3).
- x+2y=2 and 2x+y=7: multiply first by 2: 2x+4y=4, subtract second: (2x+4y)−(2x+y)=4−7⇒3y=−3⇒y=−1, then x=4. Point C(4,−1).
Step 2 – Compute area using determinant formula
Area of triangle with vertices (x1,y1),(x2,y2),(x3,y3): …
The three lines form a triangle. The area is found by computing the vertices (intersection points) and applying the coordinate area formula. The area is 6 square units.
Concept and Intuition
When three non-parallel lines are drawn in a plane, they typically enclose a triangle — unless two are parallel or all three meet at a single point. The problem asks for the area bounded by these three lines, which means the region common to all three constraints. That region is a triangle whose vertices are the pairwise intersections of the lines.
The standard approach: find the three intersection points, then use the determinant (shoelace) formula for the area of a triangle given its vertices. This is cleaner than trying to integrate, since the boundaries are straight lines.
Always check whether any two lines are parallel before solving. If the slopes match, the region might be unbounded or a strip — but here all slopes are different, so a triangle is guaranteed.
Step-by-step solution
1. Write the equations in a convenient form
We have:
L1L2L3:x+2y=2:y−x=1⇒y=x+1:2x+y=7
2. Find the intersection points (vertices)
- Intersection of L1 and L2: Substitute y=x+1 into x+2y=2:
x+2(x+1)=2⇒3x+2=2⇒x=0
Then y=0+1=1.
Vertex A=(0,1).
- Intersection of L2 and L3: Substitute y=x+1 into 2x+y=7:
2x+(x+1)=7⇒3x=6⇒x=2
Then y=2+1=3.
Vertex B=(2,3).
- Intersection of L1 and L3: Solve the system:
{x+2y=22x+y=7
Multiply the first equation by 2: 2x+4y=4. Subtract the second equation:
(2x+4y)−(2x+y)=4−7⇒3y=−3⇒y=−1
Then from x+2(−1)=2, we get x=4.
Vertex C=(4,−1).
So the three vertices are A(0,1), B(2,3), C(4,−1).
A common mistake is to mislabel which lines intersect where. Always solve each pair explicitly — don't assume the order.
3. Compute the area using the shoelace formula …
Method: Area enclosed by three straight lines
When three non-parallel lines bound a region, that region is a triangle; the cleanest route is to locate its three corners and apply the coordinate-geometry area formula.
Steps
Step 1: Confirm a triangle is actually formed.
Check that no two lines share the same slope — parallel lines would leave the region open and unbounded. Three different slopes guarantee three distinct corners.
Step 2: Find the vertices by solving the lines in pairs.
Each corner is the intersection of two of the lines, so solve all three pairs simultaneously. This gives vertices (x1,y1), (x2,y2), (x3,y3).
Step 3: Apply the shoelace (determinant) formula.
A=21∣x1(y2−y3)+x2(y3−y1)+x3(y1−y2)∣. …
Common Mistakes
Mistake 1: Setting up integrals instead of using the triangle.
Why it's wrong: three non-parallel lines enclose a triangle, so once the vertices are known the area is a single shoelace computation — integrating is longer and error-prone here. Correct approach: find the three pairwise intersections, then apply 21∣x1(y2−y3)+x2(y3−y1)+x3(y1−y2)∣.
Mistake 2: Pairing the wrong lines when finding vertices. …
Showing the 12 most recent of 20 on this concept.
- AP EAPCET 2023Set eng-2023-05-18-AN1 markMCQQ.The area bounded by y−1=−∣x∣ and y+1=∣x∣ is (A) 21 (B) 1 (C) 2 (D) 0
›Reveal solutionSolution
The two absolute-value "V" graphs cross at (±1,0) and enclose a rhombus-shaped region (a square rotated 45°) of area 2.
Concept and Intuition
y−1=−∣x∣⇒y=1−∣x∣ is an upside-down V peaking at (0,1) with slopes ∓1. y+1=∣x∣⇒y=∣x∣−1 is a right-side-up V bottoming at (0,−1) with slopes ±1. Since both have unit slopes, the enclosed figure is actually a square with diagonals along the axes (vertices at (0,1),(1,0),(0,−1),(−1,0)), i.e. a rhombus/square of diagonal length 2 each way.
Step-by-Step Solution
- Find intersections: 1−∣x∣=∣x∣−1⇒2=2∣x∣⇒∣x∣=1⇒x=±1, giving points (1,0) and (−1,0).
- On (−1,1), the top curve is y=1−∣x∣ (value 1 at x=0) and the bottom curve is y=∣x∣−1 (value −1 at x=0).
- Area =∫−11[(1−∣x∣)−(∣x∣−1)]dx=∫−11(2−2∣x∣)dx. …
- AP EAPCET 2026Set eng-2026-05-13-FN1 markMCQQ.The area of the region bounded by the curve y=x2+x, the lines y=x, x=1 and y=2 is (A) 512 (B) 27 (C) 54 (D) 31
›Reveal solutionSolution
The four boundary curves pin down a single closed loop from x=0 to x=1 between the parabola and the line y=x; its area is 31.
Concept and Intuition
When several curves are said to "bound a region," first locate every pairwise intersection — the closed loop's vertices are exactly these intersection points, and its area is found by integrating (upper curve minus lower curve) over the right interval.
Step-by-Step Solution
- Intersection of y=x2+x and y=x: x2+x=x⇒x2=0⇒x=0. They only touch at (0,0), and since x2+x−x=x2≥0, the parabola is above the line for all other x.
- Intersection of y=x and x=1: point (1,1).
- Intersection of y=x2+x and x=1: point (1,2).
- Intersection of y=x2+x and y=2: x2+x−2=0⇒(x−1)(x+2)=0⇒x=1 (the relevant root, giving (1,2) again). …
- AP EAPCET 2025Set eng-2025-05-23-FN1 markMCQQ.The area (in sq. units) of the region bounded by the lines x=0, x=2π and f(x)=sinx, g(x)=cosx is (A) 2(2−1) (B) 2(3−1) (C) 2(2+1) (D) 32+1
›Reveal solutionSolution
The two curves sinx and cosx cross at x=π/4 inside [0,π/2], so the enclosed area is the sum of two pieces, each evaluating to 2−1, giving total 2(2−1).
Concept and Intuition
Since sinx and cosx swap which one is larger at x=π/4, the area between them over [0,π/2] must be split at that crossing point and the absolute difference integrated on each side.
Step-by-Step Solution
- On [0,π/4]: cosx≥sinx, so area contribution is ∫0π/4(cosx−sinx)dx=[sinx+cosx]0π/4=(22+22)−(0+1)=2−1. …
- AP EAPCET 2023Set eng-2023-05-16-FN1 markMCQQ.The area bounded by the curves y−1=cosx, y=sinx and the X-axis between x=0 and x=π is (A) 2+2π (B) −2π (C) 2−2π (D) 2π
›Reveal solutionSolution
The area of the region bounded by y=1+cosx, y=sinx and the X-axis on [0,π] is 2π.
Concept and Intuition
Three curves fence off one closed region above the X-axis. Its floor is y=0; its roof is whichever curve is lower at each x (the lower envelope), because that is what actually caps the region touching the axis. So the area is the integral of min(1+cosx, sinx).
Step-by-Step Solution
- Find the crossing: 1+cosx=sinx⇒sinx−cosx=1⇒2sin(x−4π)=1, giving x=2π and x=π.
- On [0,2π]: at x=0, sinx=0<1+cosx=2, so sinx is the lower (roof) curve.
- On [2π,π]: at x=43π, 1+cosx≈0.29<sinx≈0.71, so 1+cosx is the roof.
- ∫0π/2sinxdx=[−cosx]0π/2=1.
- ∫π/2π(1+cosx)dx=[x+sinx]π/2π=π−(2π+1)=2π−1. …
- AP EAPCET 2024Set eng-2024-05-22-FN1 markMCQQ.The area (in sq. units) bounded by the curves x=y2 and x=3−2y2 is (A) 8 (B) 38 (C) 4 (D) 6
›Reveal solutionSolution
Integrate horizontally (with respect to y) since both curves are given as x= function of y. Answer: 4 square units.
Concept and Intuition
Both curves open sideways (they're expressed as x in terms of y), so it's natural to integrate along y, treating the region as bounded on the right by x=3−2y2 and on the left by x=y2, between their points of intersection.
Step-by-Step Solution
- Find intersection points: set y2=3−2y2⇒3y2=3⇒y2=1⇒y=±1.
- For −1≤y≤1, check which curve is to the right: at y=0, x=y2=0 vs x=3−2y2=3, so 3−2y2≥y2 throughout this range.
- Area =∫−11[(3−2y2)−y2]dy=∫−11(3−3y2)dy. …
- AP EAPCET 2026Set eng-2026-05-12-FN1 markMCQQ.The area of the region bounded by the curve xy=−a (a>1) and the lines x=−a and y=a is (A) a(a−1−loga) (B) a(a+1+loga) (C) a2−a+loga (D) a2−a−loga
›Reveal solutionSolution
The area enclosed by the rectangular hyperbola xy=−a and the lines x=−a, y=a works out, after a direct integration, to a(a−1−loga).
Concept and Intuition
xy=−a (a>0) is a hyperbola lying in the second and fourth quadrants (since the product of coordinates must be negative). We only need the branch in the second quadrant here (x<0,y>0, i.e. y=−a/x). The two given lines pin down a finite region between the curve and the corner point where the lines would meet.
Step-by-Step Solution
- Rewrite the curve as y=−xa (valid for x<0 here, giving y>0).
- Find where the curve meets x=−a: y=−a/(−a)=1, point (−a,1).
- Find where the curve meets y=a: a=−a/x⇒x=−1, point (−1,a).
- For x∈[−a,−1], the curve y=−a/x lies below the line y=a (check at x=−1: curve value =a, equal; at x=−a: curve value=1<a since a>1). So the vertical strip between the curve and the top line y=a, from x=−a to x=−1, is exactly the bounded region.
- Area =∫−a−1[a−(−xa)]dx=∫−a−1(a+xa)dx. …
- AP EAPCET 2026Set eng-2026-05-14-AN1 markMCQQ.The area of the region enclosed between the curve y=loge(x+e) and the coordinate axes is (A) 4 (B) 3 (C) 2 (D) 1
›Reveal solutionSolution
The region bounded by y=log(x+e) and the two coordinate axes is a simple region between x=1−e (where the curve meets the x-axis) and x=0 (where it meets the y-axis); the area works out to exactly 1.
Concept and Intuition
To find the area enclosed between a curve and the coordinate axes, first locate where the curve crosses each axis — those crossing points bound the finite region. Here y=log(x+e) is a shifted, increasing logarithm; it crosses the y-axis at x=0 (giving y=loge=1) and the x-axis where log(x+e)=0, i.e. x+e=1, so x=1−e. Since the curve is positive throughout (1−e,0), the enclosed area is simply the definite integral of y over that interval.
Step-by-Step Solution
- Find the y-axis intercept: at x=0, y=log(0+e)=loge=1.
- Find the x-axis intercept: set log(x+e)=0⇒x+e=1⇒x=1−e (note 1−e≈−1.718).
- For x∈(1−e,0), the curve is increasing from 0 up to 1, staying non-negative, so the enclosed area is Area=∫1−e0log(x+e)dx. …
- AP EAPCET 2023Set eng-2023-05-16-AN1 markMCQQ.The area bounded by the curve x=log(∣y∣), the lines x=−1 and x=0 is (A) 1−e−1 (B) 1−e (C) 2(1−e) (D) 2(1−e−1)
›Reveal solutionSolution
The curve x=log∣y∣ has two branches y=±ex; the area enclosed between x=−1 and x=0 is 2(1−e−1).
Concept and Intuition
x=log∣y∣⇔∣y∣=ex⇔y=±ex, giving a symmetric pair of curves about the x-axis.
Step-by-Step Solution
- Upper branch: y=ex. Lower branch: y=−ex.
- Between x=−1 and x=0, the vertical gap between the branches is ex−(−ex)=2ex. …
- AP EAPCET 2024Set eng-2024-05-21-FN1 markMCQQ.The area of the region under the curve y=∣sinx−cosx∣, 0≤x≤2π and above x-axis, is (in square units) (A) 22 (B) 22−1 (C) 2(2−1) (D) 2(2+1)
›Reveal solutionSolution
Split the region at x=π/4 where sinx=cosx, integrate each branch of the absolute value separately, and add.
Concept and Intuition
∣sinx−cosx∣ is cosx−sinx for x<π/4 (where cosine dominates) and sinx−cosx for x>π/4 (where sine dominates) — the area under an absolute-value curve must be computed piecewise across the sign change.
Step-by-Step Solution
- sinx=cosx at x=π/4 within [0,π/2]; for x<π/4, cosx>sinx, so ∣sinx−cosx∣=cosx−sinx; for x>π/4, it's sinx−cosx.
- ∫0π/4(cosx−sinx)dx=[sinx+cosx]0π/4=(22+22)−(0+1)=2−1. …
- AP EAPCET 2023Set eng-2023-05-18-FN1 markMCQQ.The area (in sq. units) bounded by the curves y=x8, y=2x and x=4 is (A) 12−8log2 (B) 12+8log2 (C) 12−8log4 (D) 12+8log4
›Reveal solutionSolution
The region enclosed by y=8/x, y=2x and x=4 runs from their intersection at x=2 to x=4, with y=2x as the upper boundary; the area works out to 12−8log2.
Concept and Intuition
Finding where the two curves meet tells us where the 'wedge'-shaped bounded region starts; the vertical line x=4 closes it off on the right. Between the intersection and the line, we need to know which curve is higher to set up ∫(upper−lower)dx correctly.
Step-by-Step Solution
- Find the intersection of y=8/x and y=2x: 8/x=2x⇒x2=4⇒x=2 (taking the positive root, matching the given curves), giving y=4.
- Determine which curve is on top between x=2 and x=4: at x=3, y=2x=6 while y=8/x≈2.67. So 2x>8/x here — the line is above the hyperbola on this interval.
- Set up the area integral from the intersection point to the line x=4: Area=∫24(2x−x8)dx.
- Antiderivative: ∫(2x−x8)dx=x2−8logx. …
- AP EAPCET 2026Set eng-2026-05-15-AN1 markMCQQ.The area enclosed between the curves y2=x and y=∣x∣ is (A) 61 (B) 31 (C) 21 (D) 32
›Reveal solutionSolution
Because y2=x only exists for x≥0, y=∣x∣ effectively reduces to the single ray y=x there; the enclosed area between the parabola and this line, from (0,0) to (1,1), is 61.
Concept and Intuition
y=∣x∣ is a V-shaped pair of rays, but the parabola y2=x only exists where x≥0 (since y2 can't be negative). So on the left half (x<0) there is no parabola to intersect the left ray of ∣x∣ — the only relevant intersection is between the parabola and the right ray y=x (x≥0). This reduces the problem to the classic area between y2=x and y=x.
Step-by-Step Solution
- Find intersection points: set y=x into y2=x: x2=x⇒x=0 or x=1. Points: (0,0) and (1,1).
- On [0,1], compare x (upper parabola branch) with x (the line): at x=0.25, x=0.5>0.25=x, so the parabola is above the line throughout (0,1). …
- AP EAPCET 2026Set eng-2026-05-18-FN1 markMCQQ.The Area (in sq. units) of the region bounded by x=0,x=2π, X-axis, y=cosx and y=tanx is (A) 25−1+21log(25−1) (B) 23−5+log(25−1) (C) 25−1−log(25−1) (D) 23−5+21log(25+1)
›Reveal solutionSolution
Since tanx→∞ at π/2, the finite region is bounded above by the lower of cosx and tanx; splitting the integral at their intersection point gives 23−5+21log25+1.
Concept and Intuition
cosx and tanx cross exactly once in (0,π/2). Since tanx diverges as x→π/2−, a region bounded by the upper envelope of the two curves would have infinite area; the sensible, finite area bounded by the x-axis and both curves on [0,π/2] is the area under whichever curve is lower at each x — i.e. under tanx before the crossing and under cosx after it.
Step-by-Step Solution
- Find the crossing point: cosx=tanx=cosxsinx⇒cos2x=sinx⇒1−sin2x=sinx⇒sin2x+sinx−1=0.
sinx0=2−1+5=s(taking the root in [0,1]).
Note also cos2x0=sinx0=s (directly from the defining equation), so cosx0=s.
2. Near x=0: cos0=1>tan0=0, so cosx is the upper curve, tanx the lower, for x∈(0,x0).
Near x=π/2: tanx→∞>cosx→0, so tanx is upper, cosx lower, for x∈(x0,π/2).
3. The finite bounded area is therefore
A=∫0x0tanxdx+∫x0π/2cosxdx.
- First piece: ∫0x0tanxdx=[−log(cosx)]0x0=−log(cosx0)=−logs=−21logs.
- Second piece: ∫x0π/2cosxdx=[sinx]x0π/2=1−sinx0=1−s. …
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