Question

If $x+y=k$ is a tangent to the hyperbola $x^2-2y^2=18,$ then sum of squares of possible values of $k$ is

• A. $3$
• B. $9$
• C. $12$
• D. $18$

Answer 1

Answer: (D)

$\frac{x^2}{18}-\frac{y^2}{9}=1$
Equation of Tangent : $y=-x+k$
$\therefore k^2=18(-1-9$
$k=\pm 3$