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How do you find the derivative of ln(tanx)?

Answer
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Hint:The given function is a composite function that is a function that consists of another function or the argument of a function is another function. Composite functions can be differentiated with the help of chain rule, let us take an example of a composite function f(x)=h(g(x)), its derivative will be given as follows:
d(f(x))dx=d(h(g(x))d(g(x))×d(g(x))dx

Formula used:
Chain rule: If a function f(x) is composition of various function as followsf(x)=g1(g2(g3(....g1(x)))) then d(f(x))dx=d(g1(g2(g3(....gn(x)))))d(g2(g3(....gn(x))))×d(g2(g3(....gn(x))))d(g3(....gn(x)))×d(g3(....gn(x)))d((....gn(x))×......×d(gn(x))dx
Derivative of logarithm function: dlnxdx=1x
And derivative of tangent function: dtanxdx=sec2x

Complete step by step answer:
In order to find the derivative of the function f(x)=ln(tanx), we have to use chain rule because this is a composite function, tangent function is the argument of the logarithmic function in this given composite function. Let us understand chain rule in order to solve this problem.If a function f(x) is composition of various function as follows
f(x)=g1(g2(g3(....g1(x)))) then its derivative will be given as
d(f(x))dx=d(g1(g2(g3(....gn(x)))))d(g2(g3(....gn(x))))×d(g2(g3(....gn(x))))d(g3(....gn(x)))×d(g3(....gn(x)))d((....gn(x))×......×d(gn(x))dx
In the given function
f(x)=ln(tanx)
Taking derivative both sides with respect to x
d(f(x))dx=d(ln(tanx))dx
Now applying chain rule to the given function f(x)=ln(tanx), we will get
d(f(x))dx=d(ln(tanx))d(tanx)×d(tanx)dx
We know that,
dlnxdx=1xanddtanxdx=sec2x
So simplifying the derivatives further with help of this,
d(f(x))dx=1tanx×sec2xd(f(x))dx=sec2xtanx
You can left it like this or should simplify it further in sine and cosine as follows
d(f(x))dx=sec2xtanxd(f(x))dx=1sinxcosx×cos2xd(f(x))dx=1sinxcosx=cscxsecx
Therefore the desired derivative of f(x)=ln(tanx) is equal to cscxsecx.

Note: When applying the chain rule in a more complex composite function then do the calculations or simplification stepwise, because chain rule also becomes complex for complex composite functions and your one mistake will change the whole answer.
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