Question

x^2+10x=-21

Answer 1

x^2 + 10x + 21 = 0
(x + 3)(x + 7) = 0
x + 3 = 0
x = -3

x + 7 = 0
x = -7

x = -3, -7

Answer 2

\[x^2+10x=-21\]
\[(x+5)^2=-21+5^2=-21+25=4\]
\[x+5=2\] or
\[x+5=-2\]
\[x=-3\] or
\[x=-7\]