How do you solve the equation x^2+3x-18=0 by completing the square?
1 Answer
Jan 8, 2017
Explanation:
The difference of squares identity can be written:
a^2-b^2 = (a-b)(a+b)
Use this with
0 = 4(x^2+3x-18)
color(white)(0) = 4x^2+12x-72
color(white)(0) = (2x)^2+2(2x)(3)+9-81
color(white)(0) = (2x+3)^2-9^2
color(white)(0) = ((2x+3)-9)((2x+3)+9)
color(white)(0) = (2x-6)(2x+12)
color(white)(0) = (2(x-3))(2(x+6))
color(white)(0) = 4(x-3)(x+6)
Hence:
x = 3" " or" "x=-6
