D=∫[(20/(1+x2))-2]dx for -3≤x≤3. This is the area between the curve and the x-axis because the expression is zero when x=-3 or 3, so the extremes of the integral are at (-3,0) and (3,0), and the whole area is above the x-axis.
D=[20tan-1(x)-2x]-33=(20tan-1(3)-6)-(20tan-1(-3)+6)=
20tan-1(3)-6-(-20tan-1(3)+6)=20tan-1(3)-6+20tan-1(3)-6=
40tan-1(3)-12=37.9618 approx.