The second small problem, cotx=cosx/sinx, the equivalent infinitesimal of X is sinx, so it is equal to cosx(x approaches 0)= 1.
The third small problem, Cos2x = COS square x of COS-the square x of SIN, so the molecule is equal to the square x of 2sin, and finally equals 2.
The fourth small problem, first exclude a sinx, then the above aspect is 1- 1/cosx, and the following is the square of x, and then you can find it with the above formula, because the process is a bit long, so I won't say much.
The fifth question, multiply up and down by 3, and then it comes out.
The sixth small question, the n power of 2 is thrown to the denominator, and the n power of 2 is one third. Then the numerator and denominator are multiplied by x at the same time, and the final answer is X.