ANSWER 27π⋅(1010−1)≅3.5631
EXPLANTION
If f′(x) is continuous on [a,b] and the curve y=f(x) is rotated about x-axis , the area of the surface of revolution so generated is
S=2π∫ab∣f(x)∣1+(f′(x))2dx
Let f(x)=x3 , a=0,b=1 , then f′(x)=3x2 and
S=2π∫01x31+9x4dx
Calculate the integral using the substitution 1+9x4=t . So, since 36x3dx=dt , we have
S=362π∫0136x31+9x4dx==18π∫110tdt=18⋅32π⋅[t23]110=18⋅32π⋅1010−18⋅32π=27π⋅(1010−1)≅3.5631
Comments