How do you solve #x^2 + 4x - 9 = 0# by completing the square?
1 Answer
Jan 11, 2017
Explanation:
The difference of squares identity can be written:
#a^2-b^2 = (a-b)(a+b)#
Hence we find:
#0 = x^2+4x-9#
#color(white)(0) = x^2+4x+4-13#
#color(white)(0) = (x+2)^2-(sqrt(13))^2#
#color(white)(0) = ((x+2)-sqrt(13))((x+2)+sqrt(13))#
#color(white)(0) = (x+2-sqrt(13))(x+2+sqrt(13))#
Hence:
#x = -2+-sqrt(13)#
