Q.The area of the region bounded by the curve x=2y+3 and the lines y=1 and y=−1 is
(A) 4 sq units
(B) 23 sq units
(C) 6 sq units
(D) 8 sq units
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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: …
Idea: The boundary is given as x=2y+3, so integrate with respect to y between the horizontal lines y=−1 and y=1 (the region between this line and the y-axis). On this interval x=2y+3 stays positive. …
The area bounded by the line x=2y+3 and the horizontal lines y=1 and y=−1 is 6 square units — option (C).
Read the boundaries
The curve is written as x=2y+3 — x in terms of y — and the limits given are horizontal lines y=−1 and y=1. That is the signal to integrate with respect to y, measuring the strip out to the line from the y-axis. On −1≤y≤1 the value x=2y+3 ranges from 1 to 5, always positive, so no absolute value is needed.
Set up the integral
Area=∫−11(2y+3)dy.
Evaluate …
Method: Area bounded by x=f(y) between two horizontal lines
Use this when the boundary is given as x in terms of y and the limits are horizontal lines y=c and y=d — the signal to integrate with respect to y.
Steps
Step 1: Recognise the natural variable.
When the curve is written as x=f(y) and the bounds are y-values, integrate in y — the horizontal strip runs from the y-axis out to the curve, of width x=f(y).
Step 2: Check the sign of f(y) on [c,d]. …
Common Mistakes
Mistake 1: Trying to integrate with respect to x.
Why it's wrong: the boundary is given as x=2y+3 with horizontal limits y=±1; converting to y=2x−3 and integrating in x needlessly complicates a clean horizontal strip and invites limit errors. Correct approach: integrate in y directly, ∫−11(2y+3)dy.
Mistake 2: Mishandling the negative lower limit. …
Showing the 12 most recent of 16 on this concept.
- KEAM 2025Set eng-2025-04294 marksMCQQ.Area of the region bounded by y=∣x∣ and x=4 is (A) 4 sq.units (B) 6 sq.units (C) 8 sq.units (D) 12 sq.units (E) 13 sq.units
›Reveal solutionSolution
The region under y=∣x∣ up to x=4 (first-quadrant triangle) has area 21×4×4=8 sq. units.
Setting up the region. The curve y=∣x∣ for x≥0 is the straight line y=x. Bounded by the x-axis and the vertical line x=4, this traces a right triangle with vertices (0,0), (4,0) and (4,4).
Computing the area. …
- KEAM 2025Set eng-2025-04264 marksMCQQ.The area bounded by y=x−1,1≤x≤2,y=0 (in sq.units) is (A) 2 (B) 1 (C) 21 (D) 4 (E) 41
›Reveal solutionSolution
Integrate x−1 from 1 to 2.
On [1,2] the line y=x−1 is nonnegative, so the area between it and y=0 is …
- KEAM 2026Set eng-2026-04184 marksMCQQ.The area of the region bounded by y=x, y=−x, and x=4 (in square units) is (A) 38 (B) 320 (C) 340 (D) 326 (E) 332
›Reveal solutionSolution
Between x=0 and x=4 the upper curve is y=x and the lower is y=−x; integrating their difference gives 340.
For 0≤x≤4, y=x lies above y=−x, so
A=∫04(x−(−x))dx=∫04(x+x)dx=[32x3/2+2x2]04. …
- KEAM 2026Set eng-2026-04214 marksMCQQ.The area of the region bounded by the lines, y=x+2, x=0, x=1 and y=0 is (A) 2 sq.units (B) 25 sq.units (C) 29 sq.units (D) 9 sq.units (E) 12 sq.units
›Reveal solutionSolution
The region is under y=x+2 from x=0 to 1; its area is ∫01(x+2)dx=25.
On [0,1] the line y=x+2 lies above y=0. The bounded area is
∫01(x+2)dx=[2x2+2x]01=21+2=25 sq. units. …
- KEAM 2024Set eng-2024-06094 marksMCQQ.The area bounded by the curves y=2x and y=x2 (in square units) is (A) 32 (B) 31 (C) 34 (D) 23 (E) 0
›Reveal solutionSolution
The line and parabola meet at x=0,2; between them the line is above, so the area is ∫02(2x−x2)dx=34.
Setting 2x=x2 gives x=0 and x=2. On (0,2), 2x>x2, so …
- KEAM 2024Set eng-2024-06074 marksMCQQ.The area bounded by the parabola y=x2+4 and the straight line passing through the points (−1,2) and (1,6) is (in square units) (A) 320 (B) 34 (C) 38 (D) 316 (E) 314
›Reveal solutionSolution
Find the line, its intersections with the parabola, and integrate the gap.
Slope of the line =1−(−1)6−2=2, so y−6=2(x−1)⇒y=2x+4.
Intersections with y=x2+4:
x2+4=2x+4⇒x2−2x=0⇒x=0,2.
On (0,2) the line lies above the parabola (at x=1: line 6, parabola 5): …
- KEAM 2024Set eng-2024-06054 marksMCQQ.The area bounded by the curves y=x2 and y=2x in the first quadrant, is equal to (A) 32 (B) 34 (C) 31 (D) 38 (E) 37
›Reveal solutionSolution
Intersection at x=0,2; integrate the difference of the upper and lower curves.
Set x2=2x⇒x=0 or x=2. On (0,2) the line y=2x lies above y=x2. So …
- KEAM 2022Set eng-2022-P2-B14 marksMCQQ.The area bounded by the curve y=x(2−x) and the line y=x is (A) 61 (B) 31 (C) 21 (D) 65 (E) 32
›Reveal solutionSolution
The enclosed area is 61.
Concept and Intuition
Find the intersection points, determine which curve is on top, then integrate the difference between them.
Step-by-Step Solution
- Set x(2−x)=x⇒2x−x2=x⇒x−x2=0⇒x=0,1.
- At x=0.5: parabola =0.75, line =0.5, so parabola is above.
- Area =∫01[(2x−x2)−x]dx=∫01(x−x2)dx. …
- KEAM 2021Set eng-2021-P2-B14 marksMCQQ.The area of the region bounded by the curves y=x2 and y=x is (in square units) (A) 32 (B) 31 (C) 61 (D) 65 (E) 1
›Reveal solutionSolution
The enclosed area between y=x2 and y=x is 31.
Concept and Intuition
Between their intersection points, the upper curve minus the lower curve integrated gives the area. On [0,1], x≥x2.
Step-by-Step Solution
- Intersections: x2=x⇒x4=x⇒x=0,1.
- Area =∫01(x−x2)dx. …
- KEAM 2024Set eng-2024-06064 marksMCQQ.The area bounded by the parabola y=x2+2 and the lines y=x, x=1 and x=2 is (in square units) (A) 631 (B) 629 (C) 625 (D) 617 (E) 613
›Reveal solutionSolution
Integrate (upper curve − lower line) over [1,2].
On [1,2], x2+2>x, so
A=∫12(x2+2−x)dx=[3x3+2x−2x2]12. …
- KEAM 2023Set eng-2023-P2-B24 marksMCQQ.The area of the region in the first quadrant enclosed by the curves y=x,y=−x+6 and the x-axis is (A) 722 (B) 322 (C) 12 (D) 24 (E) 8
›Reveal solutionSolution
The area is 322.
Concept and Intuition
The region is bounded on the left by y=x, on the right by the line y=−x+6, and below by the x-axis; split the x-integration at their intersection.
Step-by-Step Solution
- Intersection of y=x and y=−x+6: x=6−x⇒x=4,y=2; the line meets the x-axis at x=6.
- ∫04xdx=[32x3/2]04=316. …
- KEAM 2026Set eng-2026-04174 marksMCQQ.A curve with equation y=x3−8x2+16x meets the x-axis at the origin O and at a point A. Then the area of the region, bounded by the curve and the straight-line segment OA, is (A) 361 (B) 362 (C) 364 (D) 365 (E) 368
›Reveal solutionSolution
Factor to find the roots, then integrate from 0 to 4.
y=x3−8x2+16x=x(x−4)2, so the curve meets the x-axis at O(0,0) and A(4,0), and y≥0 on [0,4]. The area between the curve and OA (the x-axis) is …
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