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Binomial expansion question watch

1. The question is find the expansion of (1-2x)^0.5 up to the power of X^3

Ok that is 1 - x - 0.5x^2 - 0.5x^3, the next part is by subbing x = 0.01 into the expansion find the seven significant figure approximation for Root 2. ? I dont know what to do for the second bit.
2. (Original post by SunDun111)
The question is find the expansion of (1-2x)^0.5 up to the power of X^3

Ok that is 1 - x - 0.5x^2 - 0.5x^3, the next part is by subbing x = 0.01 into the expansion find the seven significant figure approximation for Root 2. ? I dont know what to do for the second bit.
If you sub in x=0.01. you'll be working out the square root of 1-0.02 = 0.98

So, the question is, how does 0.98 relate to 2.

Well, we can write 0.98 = 2 x 0.49

And we know the square root of 0.49, it's 0.7

So,

And we can work out the LHS using our expansion.

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