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Difference between revisions of "1982 AHSME Problems/Problem 20"

(Created page with "==1982 AHSME Problems/Problem 20== ==Problem== The number of pairs of positive integers <math>(x,y)</math> which satisfy the equation <math>x^2+y^2=x^3</math> is <math>\tex...")
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Revision as of 13:15, 22 August 2015

1982 AHSME Problems/Problem 20

Problem

The number of pairs of positive integers $(x,y)$ which satisfy the equation $x^2+y^2=x^3$ is

$\text {(A)} 0 \qquad \text {(B)} 1 \qquad \text {(C)} 2 \qquad \text {(D)} \text{not finite} \qquad \text {(E)} \text{none of these}$

Solution

Rearrange the equation to $y^2=x^3-x^2=x^2(x-1)$. This equation is satisfied whenever $x-1$ is a perfect square. There are infinite possible values of $x$, and thus the answer is $\boxed{D: Not Finite}$

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