Question

Find the roots of the quadratic equation x^2-8x=9 by completing the square. Show your work.

Answer 1

$x^{2} -8x=9 \\ x^{2} -8x+(-4)^{2} = 9 + (-4)^{2} \\ x^{2} -8x+16 = 9 + 16 \\ (x-4)^{2} =25 \\ x-4= \sqrt{25} \\ x-4= \pm 5 \\ x= \pm 5+4$
x = 5 + 4 or -5 + 4
x = 9 or -1