4. (17 points) Simplify each of the following expressions to a form that has no fractions. Make sure to show all the steps of your computations. (а) (4 points) \frac{\cos

^{3} x}{\sin (x)+1} \frac{1+\tan (x)}{\sin (x)+\cos (x)} \frac{\csc ^{4}(x)-\cot ^{4}(x)}{2 \cot ^{2}(x)+1} (b) (6 points) (c) (7 points)