C1 June 2014 edexcel question 10

On question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?

on question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?

On question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?

On question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?

Uh I don't understand what you're trying to say, but here's how I would calculate it.

4^-0.5 = 0.25^0.5
Sqrt(0.25) = 0.5

But surely -0.5x-0.5 also =0.25?


Posted from TSR Mobile

Whyyyy


Posted from TSR Mobile

That's correct but both $\sqrt{x}$ and $x^\frac{1}{2}$ are defined as meaning the positive square root of $x$.

So $4^{-\frac{1}{2}} = -0.25$ would be incorrect.

Did you read through the thread that BuryMathsTutor linked to?

Yes just read it... I was never taught this really I just assumed it and was never corrected so now I know thanks


Posted from TSR Mobile

Don't worry - plenty of students are not taught this and even some teachers get confused.

You're in the miniority in that you accepted the fact without argument - well done

Most people on here continue to argue for many pages of a thread, which is the reason why MrM created the sticky thread explaining it.

On question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?

On question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?

Can you post the whole question please.

4^-1/2 simply means 1 over 4^1/2 which is 1/2. The -be power simply means "one over" so think of it as (4^.05)^-1 if that makes sense? That's how i do it any way


Posted from TSR Mobile

Yes I know that but the up until now I've been told that the square root of e.g. 4 is either -2 or +2 because -2x-2 is 4 and 2x2 is also 4.


Posted from TSR Mobile

On question 10b how do you know whether 4^-1/2 = 1/2 or -1/2? Surely it could be either and therefore there are two answers to this question?