Question

Find the volume of the frustrum of the right circular cone generated by rotating the line y = 3x+1 about the x-axis between x = 0 and x = 2.

Answer 1

Answer:

38π cubic units

Step-by-step explanation:

The volume V = ∫₀²πy²dx  

Since y = 3x + 1, dy = 3dx ⇒ dx = dy/3

So, when x = 0, y = 3(0) + 1 = 0 + 1 = 1

when x = 2, y = 3(2) + 1 = 6 + 1 = 7

So, changing the variable to y and the limits of integration from y = 1 to y = 7, we have

V = ∫₀²πy²dx

V = π∫₁⁷y²dy/3

V = π[y³/3]₁⁷/3

V = π[y³]₁⁷/9

V = [7³ - 1³]π/9

V = [343 - 1]π/9

V = 342π/9

V = 38π cubic units