Q50 / 90 · JEE Main 2017 (09 Apr Online) · Mathematics

A tangent to the curve, y=fx at Px, y meets x-axis at A and y-axis at B. If AP:BP=1:3 and f1=1, then the curve also passes through the point

  • A
    13, 24
  • B
    12, 4
  • Correct answer
    C
    2,18
  • D
    3,128

Solution

Equation of tangent,

Y−y= dy dx (X−x) A( x−y dx dy ,0 )  ​:  B( 0,y−x dy dx )

Given, AP:BP=1:3,

Using section formula, we get

y=y−xdydx4

⇒y−xdydx=4y

⇒dyy+3dxx=0

By integrating w.r.t x, we get

ln|y|+3ln|x|=lnc

|yx3|=c

∵f(1)=1

∴c=1

⇒|yx3|=1

Hence, the curve passes throught the point 2,18

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

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