+0  
 
+1
980
4
avatar+124 

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! 

 Jul 15, 2020
 #1
avatar
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

 

128y7 − 2240y6 + 16800y5 − 70000y4 + 175000y3 − 262500y2 + 218750y − 78125 

 

So what is the coefficient of y4 according to that?   Looks like it's  –70,000       

.

 Jul 15, 2020
 #2
avatar+124 
+1

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

 Jul 15, 2020
 #3
avatar
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.   

.

 Jul 15, 2020
 #4
avatar
0

 

By "top result" I didn't mean the best one.  I meant it was the top one - the first one - on the list of search results. 

.

Guest Jul 15, 2020

4 Online Users

avatar
avatar
avatar