INTEG: Integral function

syntax: INTEG(expr, varname, lower, upper) or
INTEG(expr, varname, lower, upper, prec)

returns the approximate numerical integral of <expr> with respect to variable <varname> given the <upper> and <lower> bounds at which to calculate the integral and the precision <prec> to calculate up to As <prec> gets smaller, the approximation usually gets more accurate The trapezoid rule is used for this function