y=x^2-1 ,y=0交于A(-1,0)A'(1,0)
y=x^2-1,x=0交于B(0,-1)
y=x^2-1,x=2交于C(2,3)
S1=Saba'=∫[-1,1] -(x^2-1)dx=x-x^3/3 |[-1,1]=2-2/3=4/3
S2=∫[1,2](x^2-1)dx=x^3/3-x |[1,2]=8/3-2-1/3+1=4/3
S=S1+S2=4/3+4/3=8/3