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X²+x-90=0 using completing the square method


User Barneypitt
by
7.5k points

1 Answer

3 votes

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(
(1)/(2) )x +
(1)/(4) = 90 +
(1)/(4)

(x +
(1)/(2) )² =
(361)/(4) ( take the square root of both sides )

x +
(1)/(2) = ±
\sqrt{(361)/(4) } = ±
(19)/(2) ( subtract
(1)/(2) from both sides )

x = -
(1)/(2) ±
(19)/(2) , thus

x = -
(1)/(2) -
(19)/(2) =
(-20)/(2) = - 10

x = -
(1)/(2) +
(19)/(2) =
(18)/(2) = 9

User Chali
by
6.6k points