Q.The area of the region bounded by the curve y=16−x2 and x-axis is
(A) 8 sq units
(B) 20π sq units
(C) 16π sq units
(D) 256π 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: Squaring y=16−x2 gives x2+y2=16 with y≥0 — the upper half of a circle of radius 4. Bounded below by the x-axis, the region is a semicircle. …
The curve y=16−x2 is the upper semicircle of radius 4, so the area it bounds with the x-axis is 8π square units.
Identify the curve
Square both sides: y2=16−x2, i.e. x2+y2=16. Because y=16−x2≥0, only the upper half is taken — this is the top semicircle of the circle of radius 4 centred at the origin, running from x=−4 to x=4.
Set up the area
The x-axis (y=0) closes the region below, so we want the semicircular area:
Area=∫−4416−x2dx.
Evaluate
Using ∫16−x2dx=2x16−x2+8sin−14x:
Area=[2x16−x2+8sin−14x]−44=8⋅2π−8⋅(−2π)=8π.
This is just the area of a semicircle of radius 4: 21π(4)2=8π. …
Method: Area under a square-root curve of the form y=a2−x2
Whenever the curve is y=a2−x2, recognise that squaring gives x2+y2=a2 with y≥0 — the upper half of a circle of radius a. The area it bounds with the x-axis is therefore a semicircle.
Steps
Step 1: Identify the curve.
Square both sides to reveal the circle x2+y2=a2; the positive square root keeps only the top half. Read off the radius a.
Step 2: Set the limits.
The semicircle runs from x=−a to x=a, where it meets the x-axis.
Step 3: Evaluate the integral (or use geometry). …
Common Mistakes
Mistake 1: Computing the whole circle's area, 16π.
Why it's wrong: y=16−x2 is only the upper half of x2+y2=16 (since y≥0), so together with the x-axis it encloses a semicircle, not the full disc. Taking 16π (the tempting distractor) doubles the true value. Correct approach: use half the circle area, 21π(4)2=8π. …
Showing the 12 most recent of 22 on this concept.
- GUJCET 2026Set x1 markMCQQ.The area bounded by the curve y=x∣x∣, X-axis and the ordinates x=−1 and x=1 is ______ (A) 0 (B) 32 (C) 31 (D) 34
›Reveal solutionSolution
By symmetry the area =2∫01x2dx=32.
The curve is y=x∣x∣: for x≥0, y=x2 (above the axis); for x<0, y=−x2 (below the axis). The bounded region between x=−1 and x=1 is symmetric, so the total (unsigned) area is twice the area from 0 to 1: …
- GSEB Higher Secondary Certificate (HSC) Examination 2026Set ANNUAL1 markMCQQ.The area of the region bounded by the curve y=x∣x∣, the x-axis, and the ordinates x=−1 and x=1 is ____.(a) 0(b) 1/3(c) 2/3(d) 4/3
›Reveal solutionSolution
Split the region at x=0 since y=x∣x∣ changes sign, then add both areas.
For x≥0, y=x2; for x<0, y=−x2. Both pieces lie below/above the axis symmetrically, so
…
- GSEB Higher Secondary Certificate (HSC) Examination 2026Set ANNUAL1 markMCQQ.The area of the region bounded by the curve y=sinx between x=0 and x=π is ____.(a) 1(b) 2(c) 3(d) 4
›Reveal solutionSolution
sinx≥0 on [0,π], so directly integrate.
…
- GUJCET 2025Set 031 markMCQQ.The area bounded by the curve y=sinx between x=−2π and x=2π is _____. (A) 4 (B) 2 (C) 3 (D) 1
›Reveal solutionSolution
[!TLDR]
Series current is 0.625 A, and the P-Q drop across the 32 Ω resistor is 20 V.
Concept
In a series potential divider the same current flows through both resistors, and the voltage across each is V=IR (Ohm's law).
Solution
The 64 Ω and 32 Ω resistors are in series between 60 V and 0 V, so the total resistance is
R=64+32=96 Ω,
and the current is …
- GUJCET 2025Set 031 markMCQQ.Area of the region bounded by the curve y=x3, x-axis and the ordinates x=−1 and x=2 is (A) 417 (B) 419 (C) 415 (D) 49
›Reveal solutionSolution
y=x3<0 on (−1,0) and >0 on (0,2), so add the magnitudes of the two parts. …
- GSEB Higher Secondary Certificate (HSC) Examination 2025Set ANNUAL1 markMCQQ.The area of the region, lying in the first quadrant, bounded by the circle x2+y2=4 and the lines x=0, x=2 = ____.(a) π(b) 3π(c) 2π(d) 4π
›Reveal solutionSolution
This region is exactly the quarter-disc of the circle in the first quadrant.
The circle x2+y2=4 has radius 2. Bounded by x=0 and x=2 in the first quadrant, this describes the full quarter-circle.
…
- GSEB Higher Secondary Certificate (HSC) Examination 2025Set ANNUAL1 markMCQQ.The area of the region bounded by y=sinx, between x=−2π and x=2π = ____.(a) 0(b) 2(c) 1(d) 3
›Reveal solutionSolution
sinx is an odd function, so use symmetry and take absolute value for area (sign changes at x=0).
…
- GSEB Higher Secondary Certificate (HSC) Examination 2025Set ANNUAL1 markMCQQ.The area of the region bounded by the curve y=x3, the X-axis, and the lines x=−2 and x=1 = ____.(a) −9(b) 415(c) −415(d) 417
›Reveal solutionSolution
y=x3 is negative for x<0 and positive for x>0, so split at x=0 and add the magnitudes.
∫x3dx=4x4.
∫−20x3dx=[4x4]−20=0−4=−4, magnitude 4 (curve is below the axis here).
…
- GUJCET 2024Set 131 markMCQQ.The area bounded by the curve y=cosx between x=−2π and x=2π is __________. (A) 2 (B) 1 (C) 0 (D) 4
›Reveal solutionSolution
cosx≥0 on [−π/2,π/2], so area =∫−π/2π/2cosxdx.
Concept. Since cosx≥0 throughout this interval, the area equals the plain integral. …
- GSEB Higher Secondary Certificate (HSC) Examination 2024Set ANNUAL1 markMCQQ.The area bounded by the curve y=cosx between x=2π and x=23π is ______.(a) 1(b) 2(c) 3(d) 4
›Reveal solutionSolution
Since cosx≤0 on [2π,23π], the area is the negative of the plain integral.
Area =∫π/23π/2∣cosx∣dx=−∫π/23π/2cosxdx=−[sinx]π/23π/2
…
- GSEB Higher Secondary Certificate (HSC) Examination 2024Set ANNUAL1 markMCQQ.The area bounded by the curve y=x∣x∣, x-axis and the ordinates x=0 and x=1 is given by ______.(a) 0(b) 31(c) 32(d) 34
›Reveal solutionSolution
On [0,1], x≥0 so y=x∣x∣ simplifies to y=x2.
For x∈[0,1], ∣x∣=x, so y=x⋅x=x2.
…
- GUJCET 2023Set 091 markMCQQ.Find the area of the region bounded by the line y=3−x, the X-axis and the ordinates x=2 and x=5. (A) 3 (B) 21 (C) 25 (D) 23
›Reveal solutionSolution
The line changes sign at x=3, so split the interval and add the absolute areas.
Concept. Area between a curve and the X-axis is ∫∣y∣dx; the line y=3−x meets the axis at x=3.
Solution.
∫23(3−x)dx=[3x−2x2]23=4.5−4=0.5, …
🎓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.