The number of tangents to the curve $xy-3y+2=0$ having slope 2 is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2
Given curve
$xy-3y+2=0$
Differentiate implicitly w.r.t. $x$
$x\frac{dy}{dx}+y-3\frac{dy}{dx}=0$
Group terms
$(x-3)\frac{dy}{dx}+y=0$
$\frac{dy}{dx}=\frac{-y}{x-3}$
Given slope $=2$
$2=\frac{-y}{x-3}$
$y=-2(x-3)$
$y=-2x+6$
This line must touch the curve, so substitute in curve equation
$x(-2x+6)-3(-2x+6)+2=0$
$-2x^2+6x+6x-18+2=0$
$-2x^2+12x-16=0$
$x^2-6x+8=0$
Discriminant
$D=36-32=4>0$
Two real and distinct points of contact exist.
Number of tangents $=2$