Question

If one of roots of the quadratic equation $x^2+qx-2=0$ is $1$, then $q=$

• A. $1$
• B. $2$
• C. $-2$
• D. $-1$

Answer 1

The correct option is A $1$

Given quadratic equation $x^2+qx-2=0$
For a quadratic equation of the form $a{x}^2+bx+c=0$, the sum of the roots is $-\frac{b}{a}$.
Here one of the root is $1$
Let the other root be $p$.
So here, $p+1=-\frac{q}{1}$
$\Rightarrow p=-q-1$

Also, the product of roots is $\frac{c}{a}$.
$\Rightarrow 1\times p=-2$
$\Rightarrow p=-2$
$\therefore q=2-1=1$