Question

For what value of $k$, does the equation $9x^2+y^2=k\left(x^2-y^2-2x\right)$ represents equation of a circle?

• A. $1$
• B. $2$
• C. $-1$
• D. $4$

Answer 1

The correct option is D $4$

$9x^2-k{x}^2+y^2+k{y}^2+2kx=0x^2(9-k)+y^2(1+k)+2kx=0$

for circle

$9-k=1+k$

So, $k=4$