How do you factor -9r^2 + 81? Algebra Polynomials and Factoring Factor Polynomials Using Special Products 1 Answer ProfLayton Apr 22, 2016 =-9(r-3)(r+3) Explanation: The difference of squares rule states that: a^2-b^2=(a-b)(a+b), and using this: -9r^2+81=-9(r^2-9) =-9(r^2-3^2) =-9(r-3)(r+3) Answer link Related questions How do you factor special products of polynomials? How do you identify special products when factoring? How do you factor x^3 -8? What are the factors of x^3y^6 – 64? How do you know if x^2 + 10x + 25 is a perfect square? How do you write 16x^2 – 48x + 36 as a perfect square trinomial? What is the difference of two squares method of factoring? How do you factor 16x^2-36 using the difference of squares? How do you factor 2x^4y^2-32? How do you factor x^2 - 27? See all questions in Factor Polynomials Using Special Products Impact of this question 1901 views around the world You can reuse this answer Creative Commons License