Question

Use the quadratic formula to solve $x^2-4x-8=0$.

• A. $2\pm 2\sqrt{3}$
• B. $1\pm \sqrt{3}$
• C. $3-3\sqrt{3}$
• D. None of these

Answer 1

The correct option is A $2\pm 2\sqrt{3}$

Given quadratic equation is $x^2-4x-8=0$

We know that, for a quadratic equation of the form $a{x}^2+bx+c=0$,

$x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}$

Here,

$a=1,b=-4,c=-8$

$\therefore x=\frac{-(-4)\pm \sqrt{(-4{)}^2-4(1\left)\right(-8)}}{2\left(1\right)}$

$\Rightarrow x=\frac{4\pm \sqrt{16+32}}{2}$

$\Rightarrow x=\frac{4\pm 4\sqrt{3}}{2}$

$\therefore x=2\pm 2\sqrt{3}$

Hence, option A is correct.