binomial expansions (1 Viewer)

[ozidolroks]

can someone please help me with this question ?

The coefficients of x^4 and x^5 in the expansion of (3-x)^n are equal in magnitude but opposite in sign. Find the value of n.

Thanks

 

[Trebla]

 

[ozidolroks]

回复: binomial expansions

how did u get 3n! on the numerator of the second last line ?

 

[Trebla]

It's meant to be 3 x n!. The 3 came from the result of cancelling the indices of base 3. The n! is part of the combinatorial.