Question

If $x=1$ is common root of equations $a{x}^2+ax+3=0$ and $x^2+x+b=0$, then value of $ab$ will be:

• A. $1$
• B. $3.5$
• C. $6$
• D. $3$

Answer 1

The correct option is D $3$

$a{x}^2+ax+3=0$

$x=1$ is a root of the equation

$a+a+3=0$

$2a=-3$

$a=\frac{-3}{2}$

$x^2+x+b=0$

$x=1$ is root

$1+1+b=0$

$b=-2$

$\therefore ab=\frac{-3}{2}\times -2$

$ab=3$