So, I came across a problem in my math book:

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

But I don't know how to do this correctly. My teacher looked over it and gave me a hint to solve the equation first, but there is no equation! I don't know how to get this, please, help. Thank you so much in advance!!!! I really do appreciate the help!

heartSTORM907 Jul 15, 2020

#1**0 **

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

I couldn't expand that by hand, so I went to a math website. The answer I got there was

128y^{7} − 2240y^{6} + 16800y^{5} − 70000y^{4} + 175000y^{3} − 262500y^{2} + 218750y − 78125

So what is the coefficient of y^{4} according to that? Looks like it's **–70,000**

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Guest Jul 15, 2020

#2**0 **

Thank you so so so much! May I know what math website you used? Thank you again!

heartSTORM907 Jul 15, 2020

#3**0 **

I just asked google search to expand that expression. The top result was

https://www.mathway.com/popular-problems/Algebra/218494

When the page opened there was an example (x–2y)^{5} on the screen. I just clicked on each term and changed them to (2y–5)^{7} and then clicked the arrow out on the far right of that line.

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Guest Jul 15, 2020