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# C2 maths help watch

1. Why does (sin 2x) / (cos 2x) = tan 2x . I thought the answer was tan x because the 2s cancel each other out
2. (Original post by man111111)
Why does (sin 2x) / (cos 2x) = tan 2x . I thought the answer was tan x because the 2s cancel each other out
The identity is and this is true whatever is. It could be a number like 0.2 or a variable like . In this case .

You can only cancel a number/variable from the top and bottom of a fraction if this number is a factor of the whole numerator and the whole denominator.

2 is not a factor of so you can't cancel it but 2 would be a factor of for example.
3. (Original post by man111111)
Why does (sin 2x) / (cos 2x) = tan 2x . I thought the answer was tan x because the 2s cancel each other out
Let y = 2x

Then we have siny/cosy = tany.

There is no cancelling out, which is a common misconception at a first glance.

Please make your thread titles clearer, specifying C2 is very useful and better than a large number of threads but 'C2 trig question' would be better still

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Updated: May 19, 2017
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