How do you solve #x^2 - 18x + 74 = 0# by completing the square?
1 Answer
Jun 13, 2016
Explanation:
Complete the square and use the difference of squares identity:
#a^2-b^2=(a-b)(a+b)#
with
#0 = x^2-18x+74#
#= x^2-18x+81-7#
#= (x-9)^2-(sqrt(7))^2#
#= ((x-9)-sqrt(7))((x-9)+sqrt(7))#
#= (x-9-sqrt(7))(x-9+sqrt(7))#
Hence the zeros are:
#x = 9 +-sqrt(7)#
