We know that the term 175000x^3y^4 is in the expansion, so we can use the binomial theorem formula to find n:
(2x - 5y)^n = C(n,0)(2x)^n(-5y)^0 + C(n,1)(2x)^(n-1)(-5y)^1 + ... + C(n,n)(2x)^0(-5y)^n
where C(n,k) is the binomial coefficient (n choose k).
We can
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