Question

what are the roots of the equation : x^2-10x-21=0 ?

Answer 1

Quadratic formula?

Answer 2

complete the square!

Answer 3

if the coefficient of the middle term is even easiest to complete the square
then you have less to do at the end

Answer 4

\[x^2-10x=21\]
\[(x-5)^2=21+5^2=46\]
\[x-5=\pm\sqrt{46}\]
\[x=5\pm\sqrt{46}\]