Given that a minus 6A plus 9 equals 0, try to factorize x square plus ax minus 4

Given that a minus 6A plus 9 equals 0, try to factorize x square plus ax minus 4

a^2-6a+9=0
(a-3)^2=0
a=3
x^2+ax-4
=x^2+3x-4
=(x+4)(x-1)