If the continuous curve is described by the function y = f(x), a ≤ x ≤ b, then the area is equal to integral
A=2π∫abx1+(dxdy)2dx
For given function
A=2π∫12x1+(6x)2dx=36π∫122(6x)1+(6x)2d(6x)
Substitution t=6x:
A=36π∫6122t1+t2dt
Substitution u=t2:
A=36π∫361441+udu=36π32(1+u)3∣∣14436=54π(145145−3737)=88.486
Answer
A = 88.486
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