How do you factor 4x^2 -20xy+25y^2?

2 Answers
Oct 15, 2015

(2x-5y)(2x-5y).

Explanation:

4x^2-20xy+25y^2
=4x^2-10xy-10xy+25y^2
=2x(2x-5y)-5y(2x-5y)
=(2x-5y)(2x-5y)

Oct 15, 2015

4x^2+20xy+25y^2=(2x+5y)^2

Explanation:

Use the formula for the square of a binomial: (a+b)^2=a^2+2ab+b^2.

Both 4 and 25, the coefficient of x^2 and y^2, are perfect squares. This makes us think that the whole expression could be a perfect square: 4 is 2^2, and 25 is 5^2. So, our claim is that

4x^2-20xy+25y^2 is (2x-5y)^2. Is it true? The only term to verify is -20xy, and it is indeed twice the product of 2x and -5y. So, the conjecture was right.