Answer:
x = - 10, x = 9
Explanation:
Given
x² + x - 90 = 0 ( add 90 to both sides )
x² + x = 90
To complete the square
add ( half the coefficient of the x- term )² to both sides
x² + 2(
)x +
= 90 +

(x +
)² =
( take the square root of both sides )
x +
= ±
= ±
( subtract
from both sides )
x = -
±
, thus
x = -
-
=
= - 10
x = -
+
=
= 9