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#