Q.The area bounded by the curve y=x∣x∣, x-axis and the ordinates x=−1 and x=1 is given by (A) 0 (B) 31 (C) 32 (D) 34 [Hint : y=x2 if x>0 and y=−x2 if x<0].
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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 function changes definition across the origin because of ∣x∣.
Step 1: Write the piecewise form.
For x≥0, y=x⋅x=x2.
For x<0, y=x⋅(−x)=−x2.
Step 2: The curve lies above the x-axis for x>0 and below it for x<0. Area is always positive, so we take absolute value:
Area=∫−10−x2dx+∫01x2dx=∫−10x2dx+∫01x2dx …
The key idea is to split the area into two parts because y=x∣x∣ changes sign at x=0 — the area is the sum of absolute values of the integrals on [−1,0] and [0,1], giving 32.
The function y=x∣x∣ is a classic example of a piecewise-defined function. For x≥0, ∣x∣=x, so y=x⋅x=x2. For x<0, ∣x∣=−x, so y=x⋅(−x)=−x2.
The graph is symmetric in a special way: it’s an odd function (since f(−x)=−f(x)), so the area below the x-axis on the left equals the area above the x-axis on the right. But area is always positive — we must take the absolute value of each region.
- Set up the integral for area Area bounded by y=f(x), the x-axis, and vertical lines x=a, x=b is given by
Area=∫ab∣f(x)∣dx
Here a=−1, b=1, and f(x)=x∣x∣.
- Split at x=0 because the expression changes form there
Area=∫−10∣x∣x∣∣dx+∫01∣x∣x∣∣dx
- Evaluate the right half (x≥0) For x≥0, x∣x∣=x2≥0, so ∣x2∣=x2.
∫01x2dx=[3x3]01=31
- Evaluate the left half (x<0) For x<0, x∣x∣=−x2≤0, so ∣−x2∣=x2. ∫−10x2dx=[3x3]−10=0−(−31)=31 …
Method: Area of a piecewise/odd function that changes sign
Use this for the area bounded by a function like y=x∣x∣ that is defined by different formulas on each side of a point and changes sign there.
Steps
Step 1: Resolve the modulus into pieces.
For x≥0, x∣x∣=x2; for x<0, x∣x∣=−x2. The behaviour (and sign) switches at x=0.
Step 2: Split the interval at the switch point and take the magnitude of each part.
Area=∫a0−x2dx+∫0bx2dx=∫a0x2dx+∫0bx2dx …
Common Mistakes
Mistake 1: Using the signed integral of an odd function.
Why it's wrong: y=x∣x∣ is odd, so ∫−11x∣x∣dx=0 — that is option (A) and it is the net value, not the area. Correct approach: split at x=0 and take magnitudes, giving 31+31=32.
Mistake 2: Mis-resolving the modulus. …
Showing the 12 most recent of 20 on this concept.
- 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 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 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 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 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 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 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 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 2024Set eng-2024-05-19-AN1 markMCQQ.The area (in sq. units) of the smaller region lying above the X-axis and bounded between the circle x2+y2=2ax and the parabola y2=ax is (A) 2a2(4π−32) (B) a2(4π−32) (C) a2(4π+32) (D) a2(4π2−31)
›Reveal solutionSolution
The circle and parabola meet at x=0 and x=a; integrating the gap between the (higher) circle and the (lower) parabola over [0,a] gives the smaller enclosed area a2(4π−32).
Concept and Intuition
The circle x2+y2=2ax, i.e. (x−a)2+y2=a2, is centered at (a,0) with radius a, so it passes through the origin and through (2a,0). The parabola y2=ax opens rightward from the origin. Near x=0 the circle bulges upward faster than the parabola (its upper-half slope near the origin is steeper), and they cross again at x=a — the "smaller" lens-shaped region above the x-axis is exactly the strip between the two curves over x∈[0,a].
Step-by-Step Solution
- Find intersections: substitute y2=ax into x2+y2=2ax: x2+ax=2ax⇒x2−ax=0⇒x(x−a)=0⇒x=0 or x=a.
- At x=a: y2=a⋅a=a2⇒y=±a; take y=a for the region above the x-axis. So the curves cross at (0,0) and (a,a).
- For 0<x<a, compare the upper branches: circle gives y=2ax−x2, parabola gives y=ax. Near x=0+, 2ax−x2≈2ax>ax, so the circle lies above the parabola throughout (0,a) — this strip is the smaller enclosed region.
- Area =∫0a[2ax−x2−ax]dx.
- For ∫0aaxdx=a⋅32x3/20a=a⋅32a3/2=32a2. …
- 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 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. …
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