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# Differentiating tan2x

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1. Hello,

On paper it says that the answer to differentiating tan2x is 2(sec(x))^2

Can someone explain to me how to get this answer? My answer is (sec(2x))^2 and I've got no clue where they get the 2 from..
2. Have you done the chain rule?
3. Standard chain rule. Make a substitution u = 2x and it should be obvious.
4. (Original post by rottweiler)
Hello,

On paper it says that the answer to differentiating tan2x is 2(sec(x))^2

Can someone explain to me how to get this answer? My answer is (sec(2x))^2 and I've got no clue where they get the 2 from..
Differentiating tan2x should give 2sec(2x)^2.
Such type of differentiation is explained in C3.

The general way of differentiating such an expression, tan(y), is to differentiate the part in bracket and multiply it with sec(y)^2.

Your expression is tan(2x).
Differentiating 2x gives you 2. So your differentiated expression should be 2*sec(2x)^2.

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