# Binomial Expansion Question?Watch

Thread starter 4 years ago
#21
(Original post by davros)
Are you happy that you have shown that k = 6?

Just put k = 6 into your expansion and simplify the x^3 term to cancel any fractions etc.
I think I've proved the k=6, but not sure if I've done the coefficient correctly...
0
4 years ago
#22
(Original post by iamabbie97)
I think I've proved the k=6, but not sure if I've done the coefficient correctly...
Not entirely convinced by your "proof" - it looks like you've just substituted k = 6 and checked that it works!

What you should be doing is saying that

for all x and so

and then solving for k.

For the last part, 180/4 is correct but you can simplify this
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