Difference between revisions of "1985 AIME Problems/Problem 2"
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<cmath>\frac{a^2b\pi}{3}=800\pi</cmath> | <cmath>\frac{a^2b\pi}{3}=800\pi</cmath> | ||
<cmath>\frac{ab^2\pi}{3}=1920\pi</cmath> | <cmath>\frac{ab^2\pi}{3}=1920\pi</cmath> | ||
− | Thus | + | Thus <math>a^2b=2400, ab^2=5760</math> |
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== See also == | == See also == |
Revision as of 12:29, 21 August 2019
Contents
[hide]Problem
When a right triangle is rotated about one leg, the volume of the cone produced is . When the triangle is rotated about the other leg, the volume of the cone produced is
. What is the length (in cm) of the hypotenuse of the triangle?
Solution
Let one leg of the triangle have length and let the other leg have length
. When we rotate around the leg of length
, the result is a cone of height
and radius
, and so of volume
. Likewise, when we rotate around the leg of length
we get a cone of height
and radius
and so of volume
. If we divide this equation by the previous one, we get
, so
. Then
so
and
so
. Then by the Pythagorean Theorem, the hypotenuse has length
.
Solution 2
Let ,
be the
legs, we have the
equations
Thus
See also
1985 AIME (Problems • Answer Key • Resources) | ||
Preceded by Problem 1 |
Followed by Problem 3 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
All AIME Problems and Solutions |