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| − | ==Problem==
| + | #REDIRECT [[2020 AMC 10B Problems/Problem 9]] |
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| − | How many ordered pairs of integers <math>(x,y)</math> satisfy the equation <cmath>x^{2020}+y^2=2y</cmath>
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| − | ==Solution==
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| − | Set it up as a quadratic in terms of y:
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| − | <cmath>y^2-2y+x^{2020}=0</cmath>
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| − | Then the discriminant is
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| − | <cmath>\Delta = 4-4x^{2020}</cmath>
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| − | This will clearly only yield real solutions when <math>x^{2020} \leq 1</math>, because it is always positive.
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| − | Then <math>x=-1,0,1</math>. Checking each one:
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| − | <math>-1</math> and <math>1</math> are the same when raised to the 2020th power:
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| − | <cmath>y^2-2y+1=(y-1)^2=0</cmath>
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| − | This has only has solutions <math>1</math>, so <math>(\pm 1,1)</math> are solutions.
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| − | Next, if <math>x=0</math>:
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| − | <cmath>y^2-2y=0</cmath>
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| − | Which has 2 solutions, so <math>(0,2)</math> and <math>(0,0)</math>
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| − | These are the only 4 solutions, so <math>\boxed{D}</math>
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| − | ==See Also==
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| − | {{AMC12 box|year=2020|ab=B|num-b=7|num-a=9}}
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| − | {{MAA Notice}}
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