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Find the coefficient of y^4 in the expansion of (2y-7)^5.

 Feb 14, 2021
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We can use the binomial theorem, which is explained here --> https://www.mathsisfun.com/algebra/binomial-theorem.html
 

Since we're only finding the coefficient of y4, the exponent of the y is, well 4, while the exponent of the 7 is 1 (5-4). 

This means the y4 term is 5C1 * (2y)4-71

= 5(2y)4-7

 

= -35(2y)4

 

= -560y4

Which means the coefficient of y4 is -560, which is also your answer :)

 Feb 14, 2021

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