20.1  b)  plot x,3-x
          integral 3-2x dx from 0 to 1.5
      c)  plot[{x^2/2+2,4},{x,0,2}]
          integral 4-(x^2/2+2) dx from 0 to 2
      f)  plot[{x^2,x^3},{x,0,1}]
          integral x^2-x^3 dx from 0 to 1
      g)  plot[{3/x^2,0},{x,2,3}]
          integral 3/x^2 dx from 2 to 3
      h)  plot[{sqrt(x-1),3-x,0},{x,1,3}]
          integral sqrt(x-1) dx from 1 to 2 + integral 3-x dx from 2 to 3
      i)  plot[{x^5/2,0},{x,-1,2},{y,-1,16}]
          -integral x^5/2 dx from -1 to 0 + integral x^5/2 dx from 0 to 2
      j)  plot[{x^2,-(-x)^(1/3),x^(1/3)},{x,-2,2}]
          integral x^2-x^(1/3) dx from -2 to 0 + integral x^(1/3)-x^2 dx from 0 to 1+integral x^2-x^(1/3) dx from 1 to 2
      k)  plot[{sqrt(x^4(1-x^3)),-sqrt(x^4(1-x^3))},{x,-1,2}]
          2*integral x^2*sqrt(1-x^3) dx from 0 to 1

20.2  polar plot r=2sin theta where theta from pi/4 to pi/2
      1/2*integral 4sin^2x dx from pi/4 to pi/2

20.3  polar plot r=1+cos phi where phi from 0 to 2*pi
      1/2*integral (2*(1+cos x))^2 dx from 0 to 2*pi

20.4  PolarPlot[{r=2 sin theta,r=2 cos theta},{theta,0,2pi}]
      1/2*(integral (2sin x)^2 dx from 0 to pi/4) + 1/2*(integral (2*cos x)^2 dx from pi/4 to pi/2)

20.5  PolarPlot[{r=2sin (3*theta),r=2|sin (3*theta)|},{theta,0,pi}]
      1/2*integral 4sin^2(3x) dx from 0 to pi 

20.6  PolarPlot[{r=1+cos theta,r=cos theta},{theta,0,2pi}]
      PolarPlot[{r=1+cos theta,r=cos theta},{theta,0,pi}]
      1/2*(integral (1+cos x)^2 dx from 0 to 2pi) - 1/2*(integral cos^2 x dx from 0 to pi)
 
20.7  ParametricPlot[{x=1+e^t,y=t-t^2},{t,0,1}]
      integral (t-t^2)*e^t dt from 0 to 1

20.8  ParametricPlot[{x=2*cos(t),y=3*sin(t)},{t,0,2*pi}]
      2 * integral b*sqrt(1-x^2/a^2) dx from -a to a
      integral a*b*sin^2(t) dt from 0 to 2*pi
 
20.9  ParametricPlot[{x=6(t-sin(t)),y=6(1-cos(t))},{t,0pi,2pi}]
      integral 36(1-cos(t))^2 dt from 0 to 2*pi