Q40 / 90 · JEE Main 2022 (27 Jul Shift 2) · Mathematics

Consider a curve y=yx in the first quadrant as shown in the figure. Let the area A1 is twice the area A2. Then the normal to the curve perpendicular to the line 2x-12y=15 does NOT pass through the point __

Figure​​​​​​​

  • A
    6,21
  • B
    8,9
  • Correct answer
    C
    10,-4
  • D
    12,-15

Solution

Given that A1=2A2

Now, from the graph

A1+A2=x×y-2×4=xy-8

⇒32 A1=xy-8

⇒A1=23xy-163

⇒∫4xfxdx=23xy-163

⇒fx=23xdydx+y

⇒23xdydx=y3

⇒2∫dyy=∫dxx

⇒2lny=lnx+lnc

⇒y2=cx 

As f4=2⇒c=1

So y2=x is the given curve.

Given that the slope of normal =-6

So the equation of normal will be 

y=-6x-12-6-14-63

⇒y=-6x+3+54

⇒y+6x=57

Only 10,-4 does not satisfy from the given options.

Hence, the correct answer is option: 'C'.

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