How do you do this question?

1) ∫₀¹ 2π x (x − x²) dx

4) ∫₀¹ π ((√y)² − y²) dy

Step-by-step explanation:

The solid formed is a hollow, upside down cone.  We can either use washer method or shell method to find the volume.

If we use washer method, the thickness of the washers is dy.  The outside radius is R = x₂ = √y, and the inside radius is r = x₁ = y.

Therefore, the volume of each washer is:

dV = π (R² − r²) t

dV = π ((√y)² − y²) dy

The total volume is the sum of all washers from y=0 to y=1.

V = ∫ dV

V = ∫₀¹ π ((√y)² − y²) dy

If we use shell method, the thickness of each shell is dx.  The radius of each shell is r = x.  The height of each shell is h = y₂ − y₁ = x − x².

Therefore, the volume of each shell is:

dV = 2π r h t

dV = 2π x (x − x²) dx

The total volume is the sum of all shells from x=0 to x=1.

V = ∫ dV

V = ∫₀¹ 2π x (x − x²) dx

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step-by-step explanation: