i have no idea to solve these problems. Can anyone give me the solutions? Thank you very much!!!

Explain why the following integrals are improper and determine whether they are

convergent or divergent. Evaluate those that are convergent.

a. {{{ int ( x/ root(x-1), dx, 1, 2 ) }}}

b. {{{ int ( 1/ (1+x^2), dx, -infinity, infinity ) }}}

c. {{{ int ( x(e^-3x), dx, 0, infinity ) }}}

d. {{{ int ( 1/ (x(ln^2)x), dx, pi, infinity ) }}}