Homework, pp. 90 --, #21, 47

p1=Plot[Piecewise[{{Cos[x],x<0},{0,x==0},{1-x^2,x>0}}],{x,-1,1}];
p2=ListPlot[{{0,0}},PlotStyle->PointSize[0.025]];
Show[p1,p2]

f[x_]:=(x^4-1)/(x-1)
g[x_]:=(x^2+1)(x+1)
Plot[{f[x],g[x]},{x,0,2}]

f[x_]:=(x^3-x^2-2x)/(x-2)
g[x_]:=x(x+1)
Plot[f[x],{x,1,3}]