Question

Solve for x the quadratic equation x² - 4x - 8 = 0.  
Give your answer correct to three significant figures. 

Answer 1

${\displaystyle x^2-4x-8=0}$

Comparing the above equation by ${\displaystyle a{x}^2+bx+c=0}$

 a = 1 , b = -4 , c = - 8

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

${\displaystyle x=\frac{4\pm {\sqrt{-4}}^2-4\times 1\times (-8)}{2\times 1}}$ 

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

${\displaystyle x=\frac{4\pm \sqrt{48}}{2}}$

${\displaystyle x=\frac{4\pm 6.928}{2}}$

x = 5.46 and -1.46 {approx}