Question

The value of a for which the lines $x=1$, $y=2$ and $a^{2}x+2y-20=0$ are concurrent is:

• A. 1
• B. 4
• C. -1
• D. -2

Answer 1

The correct option is B

4

Since $x=1$, $y=2$ and $a^{2}x+2y-20=0$ are concurrent
$\therefore$ $x=1$ and $y=2$ lie on the line $a^{2}x+2y-20=0$
$\Rightarrow$ $x=1$ and $y=2$ is a solution of given equation.
On substituting $x=1$ and $y=2$ in equation $a^{2}x+2y-20=0$, we get
$\Rightarrow a^2\times 1+2\times 2-20=0\Rightarrow a^2-16=0$
$\Rightarrow a^2=16\Rightarrow a=-4or4$