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Parabola question

2025 · 4 Apr · Shift 2 · Q36
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Parabola question

2025 · 4 Apr · Shift 2 · Q36

JEE MainMathematicsParabolaMCQ+4 / −1
A line passing through the point A(−2,0)\mathrm{A}(-2,0)A(−2,0), touches the parabola P:y2=x−2\mathrm{P}: y^2=x-2P:y2=x−2 at the point BBB in the first quadrant. The area, of the region bounded by the line ABA BAB, parabola PPP and the xxx-axis, is :
  1. A
    3
  2. B
    73\frac{7}{3}37​
  3. C
    83\frac{8}{3}38​
  4. D
    2
View written solutionFree

Correct answer: C

  1. Write the parabola in standard form

Given y2=x−2  ⟹  x=y2+2y^2=x-2 \implies x=y^2+2y2=x−2⟹x=y2+2 This is a right-opening parabola with vertex at (2,0)(2,0)(2,0).

The point of contact BBB lies in the first quadrant, so let B=(2+t2,t),t>0.B=(2+t^2,t), \quad t>0.B=(2+t2,t),t>0.


  1. Equation of tangent to the parabola at parameter ttt

For the parabola y2=4a(x−h),y^2=4a(x-h),y2=4a(x−h), with 4a=14a=14a=1 and h=2h=2h=2, the tangent at (2+t2,t)(2+t^2,t)(2+t2,t) can be written using differentiation.

From y2=x−2,y^2=x-2,y2=x−2, differentiate: 2ydydx=1  ⟹  dydx=12y.2y\frac{dy}{dx}=1 \implies \frac{dy}{dx}=\frac{1}{2y}.2ydxdy​=1⟹dxdy​=2y1​. So at BBB, slope of tangent is m=12t.m=\frac{1}{2t}.m=2t1​.

Hence tangent at (2+t2,t)(2+t^2,t)(2+t2,t) is y−t=12t(x−(2+t2)).y-t=\frac{1}{2t}\big(x-(2+t^2)\big).y−t=2t1​(x−(2+t2)).


  1. Use the fact that tangent passes through A(−2,0)A(-2,0)A(−2,0)

Substitute (−2,0)(-2,0)(−2,0) into the tangent equation: 0−t=12t(−2−(2+t2)).0-t=\frac{1}{2t}\big(-2-(2+t^2)\big).0−t=2t1​(−2−(2+t2)). So, −t=−4−t22t.-t=\frac{-4-t^2}{2t}.−t=2t−4−t2​. Multiply by 2t2t2t: −2t2=−4−t2-2t^2=-4-t^2−2t2=−4−t2 −t2=−4-t^2=-4−t2=−4 t2=4.t^2=4.t2=4. Since t>0t>0t>0, t=2.t=2.t=2.

Therefore, B=(2+4,2)=(6,2).B=(2+4,2)=(6,2).B=(2+4,2)=(6,2).


  1. Find equation of line ABABAB

Slope of ABABAB: m=2−06−(−2)=28=14.m=\frac{2-0}{6-(-2)}=\frac{2}{8}=\frac14.m=6−(−2)2−0​=82​=41​. Hence equation is y=14(x+2)=x4+12.y=\frac14(x+2)=\frac{x}{4}+\frac12.y=41​(x+2)=4x​+21​. Or in terms of xxx as a function of yyy: x=4y−2.x=4y-2.x=4y−2.


  1. Identify the bounded region

The region is bounded by:

  • the line segment ABABAB
  • the parabola from (2,0)(2,0)(2,0) to (6,2)(6,2)(6,2)
  • the xxx-axis from (−2,0)(-2,0)(−2,0) to (2,0)(2,0)(2,0)

It is convenient to integrate with respect to yyy from y=0y=0y=0 to y=2y=2y=2.

For a fixed y∈[0,2]y\in[0,2]y∈[0,2]:

  • left boundary is the line: x=4y−2x=4y-2x=4y−2
  • right boundary is the parabola: x=y2+2x=y^2+2x=y2+2

So area is Area=∫02[(y2+2)−(4y−2)] dy.\text{Area}=\int_0^2 \big[(y^2+2)-(4y-2)\big] \,dy.Area=∫02​[(y2+2)−(4y−2)]dy.

Simplify: Area=∫02(y2−4y+4) dy=∫02(y−2)2 dy.\text{Area}=\int_0^2 (y^2-4y+4)\,dy=\int_0^2 (y-2)^2\,dy.Area=∫02​(y2−4y+4)dy=∫02​(y−2)2dy.


  1. Evaluate the integral

Area=∫02(y2−4y+4) dy\text{Area}=\int_0^2 (y^2-4y+4)\,dyArea=∫02​(y2−4y+4)dy =[y33−2y2+4y]02=\left[\frac{y^3}{3}-2y^2+4y\right]_0^2=[3y3​−2y2+4y]02​ =(83−8+8)−0=\left(\frac{8}{3}-8+8\right)-0=(38​−8+8)−0 =83.=\frac{8}{3}.=38​.


  1. Check options

The area is 83\boxed{\frac{8}{3}}38​​ So the correct option is C.


  1. Comparison with stored answer

Stored correct answer: C

Our derived answer: C

So they agree.

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