How do you expand #(x-9y)^2#? Precalculus The Binomial Theorem Pascal's Triangle and Binomial Expansion 1 Answer Ratnaker Mehta Aug 14, 2016 #x^2-18xy+81y^2#. Explanation: We use the Formula # : (a-b)^2=a^2-2ab+b^2#. Hence, #(x-9y)^2=x^2-2*x*9y+(9y)^2# #=x^2-18xy+81y^2#. Answer link Related questions What is Pascal's triangle? How do I find the #n#th row of Pascal's triangle? How does Pascal's triangle relate to binomial expansion? How do I find a coefficient using Pascal's triangle? How do I use Pascal's triangle to expand #(2x + y)^4#? How do I use Pascal's triangle to expand #(3a + b)^4#? How do I use Pascal's triangle to expand #(x + 2)^5#? How do I use Pascal's triangle to expand #(x - 1)^5#? How do I use Pascal's triangle to expand a binomial? How do I use Pascal's triangle to expand the binomial #(a-b)^6#? See all questions in Pascal's Triangle and Binomial Expansion Impact of this question 1933 views around the world You can reuse this answer Creative Commons License