Question 70365
Factor Completely:

5a^2 - 125
First factor out the greatest common factor, 5:
5(a^2)-5(25)
5(a^2-25)
Now you have the diffence of two square {{{x^2-y^2=(x+y)(x-y)}}}, your x=a and y=5
{{{highlight(5(a+5)(a-5))}}}
To check, multiply it back out to see if you get back to where you started.
5[a(a-5)+5(a-5)]
5[a(a)+a(-5)+5(a)+5(-5)]
5(a^2-5a+5a-25)
5(a^2-25)
5(a^2)+5(-25)
5a^2-125  We're right!!!!
Happy Calculating!!!!