Factor the expression
y^2 - 900

Factoring:  y2-900  

Theory : A difference of two perfect squares,  A2 - B2  can be factored into  (A+B) • (A-B)

Proof :  (A+B) • (A-B) =

        A2 - AB + BA - B2 =

        A2 - AB + AB - B2 =

        A2 - B2

Note :  AB = BA is the commutative property of multiplication.

Note :  - AB + AB equals zero and is therefore eliminated from the expression.

Check : 900 is the square of 30

Check :  y2  is the square of  y1  

Factorization is :       (y + 30)  •  (y - 30)