# Core 4 binomial Watch

1. If I sub in x=-1 I get ½[(15)^0.25] so I can double the answer to work out
and approximation to (15)^0.25

My question is why can I not use a similar approach for x = -15.976
The answer should be 10 times too small but it doesn't work??
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2. (Original post by mrmanps)
If I sub in x=-1 I get ½[(15)^0.25] so I can double the answer to work out
and approximation to (15)^0.25

My question is why can I not use a similar approach for x = -15.976
The answer should be 10 times too small but it doesn't work??
Please post your image the correct way round. I know it looks the correct way on your computer or phone but something annoying happens and it uploads in the orientation that you took it relative to something.

But I would say remember the range of x values for which the expansion is valid and how you find it. Anything of magnitude 15 probably isn't in that range

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