Difference between revisions of "2012 AIME I Problems/Problem 6"
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==Solution== | ==Solution== | ||
| − | Substituting the first equation into the second, we find that <math>(z^{13})^{11} = z</math> and thus <math>z^{142} = 1.</math> So <math>z</math> must be a <math>142</math>nd root of unity, and thus the imaginary part of <math>z</math> will be <math>\sin{\frac{2m\pi}{142}} = \sin{\frac{m\pi}{71}}</math> for some <math>m</math> with <math>0 \le m < 142.</math> But note that | + | Substituting the first equation into the second, we find that <math>(z^{13})^{11} = z</math> and thus <math>z^{142} = 1.</math> So <math>z</math> must be a <math>142</math>nd root of unity, and thus the imaginary part of <math>z</math> will be <math>\sin{\frac{2m\pi}{142}} = \sin{\frac{m\pi}{71}}</math> for some <math>m</math> with <math>0 \le m < 142.</math> But note that <math>71</math> is prime and <math>m<71</math> by the conditions of the problem so the denominator in the argument of this value will always be <math>71</math> and thus <math>n = \boxed{071.}</math> |
== See also == | == See also == | ||
{{AIME box|year=2012|n=I|num-b=5|num-a=7}} | {{AIME box|year=2012|n=I|num-b=5|num-a=7}} | ||
Revision as of 02:10, 17 March 2012
Problem 6
The complex numbers 
and 
satisfy 
and the imaginary part of is 
, for relatively prime positive integers 
and 
with 
Find 
Solution
Substituting the first equation into the second, we find that 
and thus 
So must be a 
nd root of unity, and thus the imaginary part of will be 
for some with 
But note that 
is prime and 
by the conditions of the problem so the denominator in the argument of this value will always be and thus 
See also
| 2012 AIME I (Problems • Answer Key • Resources) | ||
| Preceded by Problem 5 |
Followed by Problem 7 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
| All AIME Problems and Solutions | ||
