$7-35.$ Use $n-$point Gauss quadrature to approximate the given integral.

$($a$){\displaystyle \underset{0}{\overset{3}{}}}{x}^{3}dx,n=2$

$($b$){\displaystyle \underset{-1}{\overset{2}{}}}{e}^{-x^2}cosxdx,n=3$

$($c$){\displaystyle \underset{-1}{\overset{1}{}}}{e}^{-x^2}sinxdx,n=4$