Improper Integrals, Infinite Limits of Integration: Integrals may have infinite limits of integration, or integrands that have singularities. Such integrals are called "improper" even though there is nothing wrong with such integrals. They may have well defined values, in which case we say they converge, or they may not, in which case we say they diverge. In this and the next problem, give the value of the integral if it converges, and enter the letter "D" if it diverges.
$\int_1^{\infty} \frac{1}{x^2}\hbox{d} x =$ .
$\int_1^{\infty} \frac{1}{x}\hbox{d} x =$ .
$\int_1^{\infty} e^{-x}\hbox{d} x =$ .
$\int_1^{\infty} e^{x}\hbox{d} x =$ .
$\int_{-\infty}^{\infty} \frac{1}{1+x^2}\hbox{d} x =$ .
$\int_{-\infty}^{\pi} e^x\hbox{d} x =$ .