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# C3 Trig help

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1. Hey guys
im stuck on a 'proof' style question - question 4 (http://www.mei.org.uk/files/papers/2011_jan_c3.pdf)
Basically, it asks you to prove sin^2(x) + cos^2(x)= 1 using a right angled triangle.

im tempted to use pythagoras - i believe this is what the mark scheme wants too but i cant figure out what to do next

it also asks for the values for which this is valid? Is this simply theta)<90?

thanks guys
2. Note that AB = AC() and CB = AC() and use Pythagoras.
3. (Original post by Parallex)
Note that AB = AC() and CB = AC() and use Pythagoras.
Great!! thanks i got it! I

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