Evaluate: \(\int^{z}_{0}(sin x - cos x) dx \hspace{1mm}

Where\hspace{1mm}letter\hspace{1mm}z = \frac{\pi}{4}. (\pi = pi)\)

Find the volume of solid generated when the area enclosed by y = 0, y = 2x, and x = 3 is rotated about the x-axis.

Find the value of x for which the function y = x\(^3\) - x has a minimum value.