x2-6x-72=0
group the terms containing x
(x2-6x)-72=0
complete the square
(x2-6x+__) get the half of 6 .. the answer is 3 .. square the 3 the answer is 9 ..
(x2-6x+9) the last term should be always positive ..
(x2-6x+9)-72-9 ..insert the 9 but it should be negative
express as a square of binomial
(x-3)2 -81=0
solve by extracting the square root
you have to square root equation above
(x-3)2 -81=0
x-3=positive negative 9 ..transpose the 3 .. it will be negative 3
x=9-3 x=3
x=-9-3 x=-12
hope i can help
