Question #326680

find the area of the surface that is generated by revolving to portion of the curve y=x^3 between x=0 and x=1 about x axis?

1
Expert's answer
2022-04-11T16:04:29-0400

ANSWER π27(10101)3.5631\frac{\pi}{27}\cdot (10\sqrt{10}-1)\cong3.5631

EXPLANTION

If f(x)f'(x) is continuous on [a,b][a,b] and the curve y=f(x)y=f(x) is rotated about x-axis , the area of the surface of revolution so generated is

S=2πabf(x)1+(f(x))2dxS =2\pi \int_{a}^{b}\left | f(x) \right |\sqrt{1+\left ( f'(x) \right )^{2}}dx

Let f(x)=x3f(x)=x^3 , a=0,b=1a=0, b=1 , then f(x)=3x2f'(x)=3x^2 and

S=2π01x31+9x4dxS =2\pi \int_{0}^{1}x^3\sqrt{1+9x^4}dx

Calculate the integral using the substitution 1+9x4=t1+9x^4=t . So, since 36x3dx=dt36x^3dx=dt , we have

S=2π360136x31+9x4dx==π18110tdt=2π183[t32]110=2π18310102π183=π27(10101)3.5631S = \frac{2\pi}{36}\int_{0}^{1}36x^3\sqrt{1+9x^4}dx=\\= \frac{\pi}{18} \int_{1}^{10}\sqrt{t}dt=\frac{2\pi}{18\cdot 3}\cdot[t^{\frac{3}{2}}]_{1} ^{10} =\frac{2\pi}{18\cdot 3}\cdot10\sqrt{10} -\frac{2\pi}{18\cdot 3} = \frac{\pi}{27}\cdot (10\sqrt{10}-1)\cong3.5631


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