washers is a good way:
v = ∫[0,16] π(R^2-r^2) dy
where R=1+|x|, r=1
v = π∫[0,16] (1+√(16-y))^2 - 1 dy
= -π(4/3 (16-y)^(3/2) + 1/2 (16-y)^2) [0,16]
= 640π/3
Or, using shells,
v = ∫[-4,0] 2πrh dx
where r=1-x and h=y
v = 2π∫[-4,0] (x+1)(16-x^2) dx
= 2πx (x^3/4 - x^2/3 - 8x + 16)[-4,0]
= 640π/3
Hmm! shells is less complicated this time.
Find the volume of the solid generated by revolving the region about the given line.
The region in the second quadrant bounded above by the curve y = 16 - x2, below by the x-axis, and on the right by the y-axis, about the line x = 1
I have gathered, that washer method is to be used - (-4,0) is the shaded area.
3 answers
Where does the 4/3 and 3/2 come from?
Thank you
Thank you
∫(1+√(16-y))^2 - 1 dy
let u = 16-y
du = -dy
∫(1+√u)^2 - 1 du
∫1 + 2√u + u - 1
∫2√u + u
2(2/3)u^(3/2) + 1/2 u^2
because
∫u^n = 1/(n+1) u^(n+1) where n=1/2
let u = 16-y
du = -dy
∫(1+√u)^2 - 1 du
∫1 + 2√u + u - 1
∫2√u + u
2(2/3)u^(3/2) + 1/2 u^2
because
∫u^n = 1/(n+1) u^(n+1) where n=1/2