2006 AIME II Problems/Problem 15
Given that and are real numbers that satisfy: and that where and are positive integers and is not divisible by the square of any prime, find
Solution 1 (Geometric Interpretation)
Let be a triangle with sides of length and , and suppose this triangle is acute (so all altitudes are in the interior of the triangle).
Let the altitude to the side of length be of length , and similarly for and . Then we have by two applications of the Pythagorean Theorem we that As a function of , the RHS of this equation is strictly decreasing, so it takes each value in its range exactly once. Thus we must have that and so and similarly and .
The area of the triangle must be the same no matter how we measure it; therefore gives us and and .
Thus, and and the answer is .
The justification that there is an acute triangle with sides of length and :
Note that and are each the sum of two positive square roots of real numbers, so . (Recall that, by AIME convention, all numbers (including square roots) are taken to be real unless otherwise indicated.)
Also, , so we have , and . But these conditions are exactly those of the triangle inequality, so there does exist such a triangle.
Solution 2 (Algebraic)
Note that none of can be zero.
Each of the equations is in the form
Isolate a radical and square the equation to get
Now cancel, and again isolate the radical, and square the equation to get
Now note that everything is cyclic but the last term (i.e. ), which implies
Plug these values into the middle equation to get
Substituting the value of for and gives
And thus the answer is
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