What is the ninth term in the binomial expansion of open paren x minus 2 y close paren to the 13th power ?

For the ninth term, use k = 8 in the binomial term formula: choose 8 factors of −2y and 5 factors of x. The coefficient is C(13, 8)(−2)^8 = 1,287 × 256 = 329,472, and the variables are x^5y^8. Since the exponent on −2 is even, the term is positive, so the answer is 329,472x^5y^8.

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