How do you find the binomial expansion of the expression $(x+3y)^7$ ?

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Answer 1 · 2015-09-10T04:31:08

You use the binomial theorem which states

$(x+y)^n=sum_(k=0)^n(n/k)x^(n-k)y^k$

So by using the binomial theorem we have that

$(x+3y)^7=x^7+21x^6y+189x^5y^2+945x^4y^3+2835x^3y^4+5103x^2y^5+5103xy^5+2187y^7$

How do you find the binomial expansion of the expression (x+3y)^7(x+3y)^7?