- #1
Aurelius120
- 151
- 16
- Homework Statement
- Evaluate the integral:
$$\int\frac{\left(1-\frac{1}{\sqrt 3}\right)(\cos x-\sin x)}{1+\frac{2}{\sqrt 3}(\sin 2x)}dx$$
- Relevant Equations
- $$\sin C+\sin D=2\sin\left(\frac{C+D}{2}\right)\cos \left(\frac{C-D}{2}\right)$$
$$\int \csc(x) dx=\ln(\csc(x)-\cot(x))$$
I proceeded as follows
$$\int\frac{2(\sqrt3-1)(cosx-sinx)}{2(\sqrt3+2sin2x)}dx$$
$$\int\frac{(cos(\pi/6)-sin(\pi/6))(cosx-sinx)}{(sin(\pi/3)+sin2x)}dx$$
$$\frac{1}{2}\int\frac{cos(\pi/6-x)-sin(\pi/6+x)}{sin(\pi/6+x)cos(\pi/6-x)}dx$$
$$\frac{1}{2}\int cosec(\pi/6+x)-sec(\pi/6-x)dx$$
Which leads to the integral in the question:
$$\frac{1}{2}\int\left[\csc\left(\frac{\pi}{6}+x\right)-\csc\left(\frac{\pi}{3}+x\right)\right]dx$$
Now the correct answer is:$$\frac{1}{2}\log\left|\frac{tan(\pi/12+x/2)}{tan(\pi/6+x/2)}\right|$$
How to reach the correct answer from the obtained integral?
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