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Calculating The Volume

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CALCULATING THE VOLUME PURE

OF A SOLID OF MATHEMATIC
REVOLUTION S
V=?
rotated about an
axis we obtain a
solid figure. This
figure is called a
solid of
revolution. We can a b
use the definite
integral to find the
volume of a solid of
revolution.
EXAMPLE 1:
What is the volume V of the solid figure generated by rotating the
area between y = 3x and the x-axis around the x-axis on the
interval [0, 2]?
EXAMPLE 2:
Find the volume of the solid figure generated by rotating the area
bounded y = 4x – 1, the x-axis, and the lines x = 1 and x = 3
around the x-axis.
EXAMPLE 3:
What is the volume V of the solid obtained by rotating the region
between y = x^2 + 2 and the x-axis around the x-axis on the
interval [1, 3]?
EXAMPLE 4:
Find the volume of the solid figure generated by rotating the area
between y = x^2 – 4 and the x-axis around the x-axis.
NOTE
If we rotate a figure around
the y-axis then the volume
is created by x = f(y) and
we integrate it with respect
to dy:
EXAMPLE 5:
Find the volume V of the solid figure generated by rotating the region
between f(x) = 3x – 1, the y-axis, and the lines y = 2 and y = 5
around the y-axis.
EXAMPLE 6:
Find the volume of the solid figure generated by rotating the area
bounded by y = 2x + 1, the y-axis, and the lines y = 2 and y = 5
around the y-axis.
NOTE
If we rotate the area
between two curves f(x)
and g(x) on the interval
[a, b] then the volume of
the solid figure
generated is:
EXAMPLE 7:
Find the volume V of the solid figure which is generated by rotating
the area of the region bounded by the graphs of y = 2x^2 + 2 and
y = 3 – 2x^2 around the x-axis.
EXAMPLE 8:
Find the volume V of the solid figure generated by rotating the area
bounded by the graphs of y = and y = around the x-axis through
60°.

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