Q.The area of the region bounded by the curve y=sinx between the ordinates x=0, x=2π and the x-axis is
(A) 2 sq units
(B) 4 sq units
(C) 3 sq units
(D) 1 sq units
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🔒 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: …
The key idea is that the area under a curve y=f(x) from x=a to x=b is given by the definite integral ∫ab∣f(x)∣dx. Since sinx≥0 on [0,2π], the absolute value is unnecessary.
Step 1: Set up the integral for the area:
A=∫0π/2sinxdx
Step 2: Integrate:
∫sinxdx=−cosx
Step 3: Evaluate the definite integral: …
The area under y=sinx from x=0 to x=π/2 is the definite integral of sinx over that interval. Since sinx≥0 on [0,π/2], the area equals ∫0π/2sinxdx=1 square unit. The correct option is (D).
The problem asks for the area bounded by the curve y=sinx, the x-axis, and the vertical lines x=0 and x=π/2. This is a classic "area under a curve" problem — but the key is to remember that area is always a positive quantity. When the curve lies above the x-axis (which sinx does on [0,π/2]), the area is simply the definite integral of the function.
Why does the integral give area? Because the definite integral ∫abf(x)dx sums up infinitely many infinitesimally thin rectangles of height f(x) and width dx. When f(x)≥0, each rectangle's height is positive, so the sum is exactly the geometric area.
Here, sinx is non-negative on [0,π/2] — it starts at 0, rises to 1 at x=π/2, and never dips below zero. So no absolute value or splitting is needed.
- Set up the integral The area A is given by
A=∫0π/2sinxdx
- Evaluate the antiderivative The antiderivative of sinx is −cosx. So
A=[−cosx]0π/2
- Apply the limits At the upper limit x=π/2: cos(π/2)=0, so −cos(π/2)=0. At the lower limit x=0: cos0=1, so −cos0=−1. Therefore …
Method: Area under a curve that stays above the x-axis
Use this for the area bounded by y=f(x), the x-axis, and two vertical ordinates, when f(x)≥0 across the whole interval (as sinx is on [0,2π]).
Steps
Step 1: Confirm the curve does not dip below the axis on [a,b].
If f(x)≥0 throughout, the signed integral already equals the geometric area — no absolute value or splitting is needed. Check the sign at a sample point (or from the known shape of the graph).
Step 2: Write the definite integral.
Area=∫abf(x)dx …
Common Mistakes
Mistake 1: Using +cosx as the antiderivative of sinx.
Why it's wrong: ∫sinxdx=−cosx, not cosx. Dropping the minus sign gives cos(2π)−cos0=−1, a negative "area." Correct approach: use [−cosx]0π/2=0−(−1)=1.
Mistake 2: Mishandling the lower-limit subtraction. …
Showing the 12 most recent of 20 on this concept.
- 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 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 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-2026-05-18-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-2023-05-15-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-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-2026-05-14-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 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-2026-05-13-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 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-2026-05-15-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 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. …
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