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# Indices watch

1. Hello, please could someone explain how to do the following question:

If y=2^x, express

i)2^2x+2 in terms of y.
ii) 2^2x+2 -21(2^x)+5

Thanks!
2. i) 2^2x+2 is the same as 2^2x * 2^2
Which is (2^x)^2 * 4
As y = 2^x so substitute into the equation
4(y^2)
3. ii) use the question before to make the equation:

4y^2 - 21y + 5 (substitute y into 2^x)

Then solve for y,

(y-5)(4y-1)

y = 5 and 0.25
4. Thank you so much! I just couldn't quite get my head around where to start. You have been a massive help!!

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Updated: March 5, 2018
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