Q.Find the area bounded by the lines y=4x+5, y=5−x and 4y=x+5.
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Area Under Curve
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 enclosed by three lines is a triangle; find its vertices by solving pairwise intersections, then use the shoelace formula or integrate.
Steps:
-
Find vertices
Intersection of y=4x+5 and y=5−x:
4x+5=5−x⇒5x=0⇒x=0, so y=5. Vertex A(0,5).
Intersection of y=4x+5 and 4y=x+5:
4(4x+5)=x+5⇒16x+20=x+5⇒15x=−15⇒x=−1, so y=1. Vertex B(−1,1).
Intersection of y=5−x and 4y=x+5:
4(5−x)=x+5⇒20−4x=x+5⇒15=5x⇒x=3, so y=2. Vertex C(3,2).
-
Area using shoelace formula …
The three lines meet at (−1,1), (0,5) and (3,2); the enclosed triangle has area 215 (i.e. 7.5) square units.
Concept
Three non-parallel, non-concurrent lines bound a triangle. Find the three pairwise intersection points, then compute the triangle's area (shoelace formula).
Solution
1. y=4x+5 and y=5−x: 4x+5=5−x⇒5x=0⇒x=0, y=5. Point A(0,5).
2. y=4x+5 and 4y=x+5: 4(4x+5)=x+5⇒16x+20=x+5⇒15x=−15⇒x=−1, y=1. Point B(−1,1).
3. y=5−x and 4y=x+5: 4(5−x)=x+5⇒20−4x=x+5⇒5x=15⇒x=3, y=2. Point C(3,2).
4. Shoelace formula with A(0,5), B(−1,1), C(3,2):
Area=21xA(yB−yC)+xB(yC−yA)+xC(yA−yB) …
Method: Area of the triangle cut out by three lines
Three lines that are pairwise non-parallel and do not all pass through one point fence off a triangular region. Find its corners, then compute the area straight from the coordinates.
Steps
Step 1: Locate the three vertices.
A vertex is where two of the lines meet, so take the lines two at a time and solve each pair. Three pairs give three corner points.
Step 2: Feed the corners into the coordinate area formula.
For vertices (x1,y1), (x2,y2), (x3,y3),
A=21∣x1(y2−y3)+x2(y3−y1)+x3(y1−y2)∣.
Step 3: Verify with base × height (optional but recommended). …
Common Mistakes
Mistake 1: Misreading 4y=x+5 as y=x+5.
Why it's wrong: forgetting to divide by 4 changes the line's slope entirely and gives wrong vertices. Correct approach: rewrite it as y=4x+5 (slope 41) before solving any intersection.
Mistake 2: Listing the vertices out of order in the shoelace formula. …
Showing the 12 most recent of 20 on this concept.
- 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 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. …
- 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 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-2023-05-15-AN1 markMCQQ.The area (in sq. units) of the region bounded by the curves y=4∣cosx∣ and y=−∣cosx∣ from x=−π/2 to π/2 is (A) 6 (B) 8 (C) 12 (D) 10
›Reveal solutionSolution
Since cosx≥0 throughout [−π/2,π/2], both curves are simple cosine multiples, and the enclosed area is 5×∫cosxdx=10.
Concept and Intuition
The area between y=f(x) (top curve) and y=g(x) (bottom curve) over an interval is ∫[f(x)−g(x)]dx. Here the vertical gap between the two curves is constant multiple of ∣cosx∣, so no case-splitting on sign is even needed within this interval.
Step-by-Step Solution
- On x∈[−π/2,π/2], cosx≥0⇒∣cosx∣=cosx.
- Top curve: y=4cosx; bottom curve: y=−cosx.
- Vertical gap: 4cosx−(−cosx)=5cosx≥0 throughout, so this is directly the integrand. …
- 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 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 2023Set eng-2023-05-17-AN1 markMCQQ.The area bounded by the curve y=x2 and y−6=−∣x∣ is (A) 37/4 (B) 22/3 (C) 44/3 (D) 38/3
›Reveal solutionSolution
The parabola and the "tent" line y=6−∣x∣ meet at x=±2; using the even symmetry of both curves, the enclosed area works out to 44/3.
Concept and Intuition
Both y=x2 and y=6−∣x∣ are even functions, so the region they enclose is symmetric about the Y-axis. It's efficient to compute the area on [0,2] (where ∣x∣=x) and double it, rather than integrating across the absolute value directly.
Step-by-Step Solution
- For x≥0: solve x2=6−x⇒x2+x−6=0⇒(x−2)(x+3)=0⇒x=2 (rejecting x=−3). By symmetry the other intersection is x=−2.
- At x=2: y=4 for both curves — consistent.
- On [0,2], the upper curve is 6−x (line) and the lower is x2 (check at x=1: line gives 5, parabola gives 1 — line is on top). …
- AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQQ.The area of the region lying between the curves y=4−x2, y2=3x and the Y-axis is (A) 3π−231 (B) 6π+231 (C) 3π+231 (D) 6π−231
›Reveal solutionSolution
Integrating with respect to y in two pieces — the parabola from y=0 to 3 and the circle from y=3 to 2 — gives the enclosed area as 3π−231.
Concept and Intuition
When a region's boundary is naturally expressed as x=x(y) for both curves (here x=4−y2 for the circle and x=y2/3 for the parabola), integrating along y with the y-axis as the common left boundary is far cleaner than integrating along x.
Step-by-Step Solution
- Find the intersection of y=4−x2 (so y2=4−x2) and y2=3x: 3x=4−x2⇒x2+3x−4=0⇒(x+4)(x−1)=0. Since x≥0 on the parabola, x=1, giving y=3.
- The circle meets the y-axis at (0,2); the parabola meets it at the origin (0,0).
- The enclosed region has: the y-axis as its left edge from (0,0) to (0,2); the parabola x=y2/3 as its right edge for y∈[0,3]; and the circle x=4−y2 as its right edge for y∈[3,2].
- Area =∫033y2dy+∫324−y2dy.
- First integral: ∫033y2dy=91[y3]03=933=33=31. …
- 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. …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.