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
🔒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: …
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 20 on this concept.
- 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-2026-05-15-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-2023-05-16-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 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 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-2023-05-17-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 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 2025Set eng-2025-05-26-AN1 markMCQQ.The area of the region (in sq.units) bounded by the curves x2+y2=16 and y2=6x is (A) 4π+43 (B) 32(4π+3) (C) 34(4π+3) (D) 34π+3
›Reveal solutionSolution
The region common to the circle x2+y2=16 and parabola y2=6x is bounded by the parabola near the origin and the circle further out; integrating each piece and doubling for symmetry gives 34(4π+3).
Concept and Intuition
The parabola y2=6x opens rightward from the origin, and the circle has radius 4. Near the vertex, the parabola is the "narrower" curve (smaller ∣y∣ for given x), so it bounds the common region; farther out, the circle becomes narrower and takes over as the boundary. The crossover is exactly at their intersection point.
Step-by-Step Solution
- Intersection: substitute y2=6x into x2+y2=16: x2+6x−16=0⇒x=2 or x=−8 (rejected, since y2=6x≥0 needs x≥0). At x=2: y2=12⇒y=±23.
- For x∈[0,2]: parabola gives smaller ∣y∣ than the circle (check at x=1: parabola ∣y∣=6≈2.45, circle ∣y∣=15≈3.87) — so the parabola bounds the region here.
- For x∈[2,4]: circle gives smaller ∣y∣ (check at x=3: parabola ∣y∣=18≈4.24, circle ∣y∣=7≈2.65) — circle bounds here.
- Area (using symmetry about the x-axis, factor 2):
A=2[∫026xdx+∫2416−x2dx].
- ∫026xdx=6⋅32x3/202=6⋅32⋅22=383.
- Using ∫16−x2dx=2x16−x2+8sin−14x: …
- 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-2026-05-12-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. …
🎓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.