Question

If the pair of linear equations $kx–y=5,x+ky=5$ has a unique solution $(x=2,y=1)$, then the value of k is ____.

• A. 2
• B. 3
• C. -3
• D. 4

Answer 1

The correct option is B

3

Substitute the value of x = 2 and y = 1 in any one of the equation

$kx–y=5$

$\Rightarrow k\left(2\right)-1=5$

$\Rightarrow 2k=6\Rightarrow k=3$

For verification, substitute k =3, x = 2 and y = 1 in the second equation.

$x+ky=5$

$2+3\left(1\right)=5\Rightarrow LHS=RHS$