Answer:
f(x) = 2π (11 + sin x) √(1 + cos²x)
Explanation:
Surface area of a curve rotated about y = a is:
S = ∫ 2π (y − a) ds,
where ds = √(1 + (dy/dx)²) dx.
y = 6 + sin x, and a = -5. dy/dx = cos x. Plugging in:
S = ∫₀²ᵖⁱ 2π (6 + sin x − -5) √(1 + cos²x) dx
S = ∫₀²ᵖⁱ 2π (11 + sin x) √(1 + cos²x) dx
Therefore, f(x) = 2π (11 + sin x) √(1 + cos²x).