How do you solve using the completing the square method x^2 + 3x – 6 = 0?

2 Answers
Jun 26, 2018

x=-3/2+-sqrt33/2

Explanation:

x^2+3x=6

x^2+2(3/2)xcolor(red)(+9/4)=6color(red)(+9/4)

(x+3/2)^2=33/4

color(blue)"take the square root of both sides"

sqrt((x+3/2)^2)=+-sqrt(33/4)larrcolor(blue)"note plus or minus"

x+3/2=+-sqrt33/2

"subtract "3/2" from both sides"

x=-3/2+-sqrt33/2larrcolor(red)"exact solutions"

Jun 26, 2018

color(brown)(x = (-1/2) (3 - sqrt33 ), -(1/2) ( 3 + sqrt33)

Explanation:

x^2 + 3x - 6 = 0

x^2 + 3x + (3/2)^2 - 6 = (3/2)^2, "adding " (3/2)^2 " to both sides"

x^2 + 2 * 3/2 * x + (3/2)^2 = (3/2)^2 + 6

(x + 3/2)^2 = 33/4

(x + 3/2)^2 = (sqrt(33/4))^2

x + 3/2 = +- sqrt(33/4), " taking squre root on both sides"

x = -3/2 +- sqrt33 / 2

color(brown)(x = (-1/2) (3 - sqrt33 ), -(1/2) ( 3 + sqrt33)