Question21. Find $\int_{1}^{\infty} \frac{1}{x} \mathrm{dx}$. a) 0 c) $-\infty$ b) 1 d) $\infty$
22. Find $\int_{1}^{\infty} \frac{2}{x^{3}} d x$. a) 0 c) 2 b) 1 d) $\infty$
23. Find $\int_{0}^{4} \frac{1}{\sqrt{4-x}} d x$. a) -4 b) 0 c) 4 d) does not exist.