Find the surface area of the body generated by the revolution around the axis of the curve defined by the parametric equations for .
If the surface area can be expressed as , where and are coprime positive integers, submit your answer as .
Bonus : Find the tangent plane to the body defined above through the point .
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We are being asked for the surface of revolution of the cardioid r = 1 + cos θ , which is S = 2 π ∫ 0 π r sin θ r 2 + ( d θ d r ) 2 d θ = 2 π ∫ 0 π ( 1 + cos θ ) sin θ 2 ( 1 + cos θ ) d θ = 2 π 2 ∫ 0 π ( 1 + cos θ ) 2 3 sin θ d θ = 2 π 2 [ − 5 2 ( 1 + cos θ ) 2 5 ] 0 π = 5 3 2 π making the answer 3 2 + 5 = 3 7 .