Equation of tangent,
Y−y=dxdy(X−x)A(x−ydydx,0):B(0,y−xdxdy)
Given, AP:BP=1:3,
Using section formula, we get
y=4y−xdxdy
⇒y−xdxdy=4y
⇒ydy+3xdx=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 (2,81)