Difference between revisions of "1996 AIME Problems/Problem 10"
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== Solution 3 (Only sine and cosine sum formulas) == | == Solution 3 (Only sine and cosine sum formulas) == | ||
− | It seems reasonable to assume that <math>\dfrac{\cos{96^{\circ}}+\sin{96^{\circ}}}{\cos{96^{\circ}}-\sin{96^{\circ}}} = \tan{\theta}</math> for some angle <math>\theta</math>. This means <cmath>\dfrac{\alpha (\cos{96^{\circ}}+\sin{96^{\circ}})}{\alpha (\cos{96^{\circ}}-\sin{96^{\circ}})} = \frac{\sin{\theta}}{\cos{\theta}}</cmath> for some constant <math>\alpha</math>. We can set <math>\alpha (\cos{96^{\circ}}+\sin{96^{\circ}) = \alpha \sin{\theta}</math>.Note that if we have <math>\alpha</math> equal to both the sine and cosine of an angle, we can use the sine sum formula (and the cosine sum formula on the denominator). So, since <math>\sin{45^{\circ}} = \cos{45^{\circ}} = \tfrac{\sqrt{2}}{2}</math>, if <math>\alpha = \frac{\sqrt{2}}{2}</math> we have <cmath>\alpha (\cos{96^{\circ}}+\sin{96^{\circ} = \cos{96^{\circ}} \frac{\sqrt{2}}{2} + \sin{96^{\circ}} \frac{\sqrt{2}}{2} = \cos{96^{\circ}} \sin{45^{\circ}} + \sin{96^{\circ}} \cos{45^{\circ}} = \sin{45^{\circ} + 96^{\circ}} = \sin{141^{\circ}}</cmath> | + | It seems reasonable to assume that <math>\dfrac{\cos{96^{\circ}}+\sin{96^{\circ}}}{\cos{96^{\circ}}-\sin{96^{\circ}}} = \tan{\theta}</math> for some angle <math>\theta</math>. This means <cmath>\dfrac{\alpha (\cos{96^{\circ}}+\sin{96^{\circ}})}{\alpha (\cos{96^{\circ}}-\sin{96^{\circ}})} = \frac{\sin{\theta}}{\cos{\theta}}</cmath> for some constant <math>\alpha</math>. We can set <math>\alpha (\cos{96^{\circ}}+\sin{96^{\circ}}) = \alpha \sin{\theta}</math>.Note that if we have <math>\alpha</math> equal to both the sine and cosine of an angle, we can use the sine sum formula (and the cosine sum formula on the denominator). So, since <math>\sin{45^{\circ}} = \cos{45^{\circ}} = \tfrac{\sqrt{2}}{2}</math>, if <math>\alpha = \frac{\sqrt{2}}{2}</math> we have <cmath>\alpha (\cos{96^{\circ}}+\sin{96^{\circ} = \cos{96^{\circ}} \frac{\sqrt{2}}{2} + \sin{96^{\circ}} \frac{\sqrt{2}}{2} = \cos{96^{\circ}} \sin{45^{\circ}} + \sin{96^{\circ}} \cos{45^{\circ}} = \sin{45^{\circ} + 96^{\circ}} = \sin{141^{\circ}}</cmath> |
from the sine sum formula. For the denominator, from the cosine sum formula, we have | from the sine sum formula. For the denominator, from the cosine sum formula, we have | ||
<cmath>\alpha (\cos{96^{\circ}} - \sin{96^{\circ}) = \cos{96^{\circ}} \frac{\sqrt{2}}{2} + \sin{96^{\circ}} \frac{\sqrt{2}}{2} = \cos{96^{\circ}} \cos{45^{\circ}} + \sin{96^{\circ}} \sin{45^{\circ}} = \cos{96^{\circ} + 45^{\circ}} = \cos{141^{\circ}}.</cmath> | <cmath>\alpha (\cos{96^{\circ}} - \sin{96^{\circ}) = \cos{96^{\circ}} \frac{\sqrt{2}}{2} + \sin{96^{\circ}} \frac{\sqrt{2}}{2} = \cos{96^{\circ}} \cos{45^{\circ}} + \sin{96^{\circ}} \sin{45^{\circ}} = \cos{96^{\circ} + 45^{\circ}} = \cos{141^{\circ}}.</cmath> |
Revision as of 15:43, 3 August 2022
Contents
Problem
Find the smallest positive integer solution to .
Solution
.
The period of the tangent function is , and the tangent function is one-to-one over each period of its domain.
Thus, .
Since , multiplying both sides by
yields
.
Therefore, the smallest positive solution is .
Solution 2
which is the same as
.
So , for some integer
.
Multiplying by
gives
.
The smallest positive solution of this is
Solution 3 (Only sine and cosine sum formulas)
It seems reasonable to assume that for some angle
. This means
for some constant
. We can set
.Note that if we have
equal to both the sine and cosine of an angle, we can use the sine sum formula (and the cosine sum formula on the denominator). So, since
, if
we have
\[\alpha (\cos{96^{\circ}}+\sin{96^{\circ} = \cos{96^{\circ}} \frac{\sqrt{2}}{2} + \sin{96^{\circ}} \frac{\sqrt{2}}{2} = \cos{96^{\circ}} \sin{45^{\circ}} + \sin{96^{\circ}} \cos{45^{\circ}} = \sin{45^{\circ} + 96^{\circ}} = \sin{141^{\circ}}\] (Error compiling LaTeX. Unknown error_msg)
from the sine sum formula. For the denominator, from the cosine sum formula, we have
\[\alpha (\cos{96^{\circ}} - \sin{96^{\circ}) = \cos{96^{\circ}} \frac{\sqrt{2}}{2} + \sin{96^{\circ}} \frac{\sqrt{2}}{2} = \cos{96^{\circ}} \cos{45^{\circ}} + \sin{96^{\circ}} \sin{45^{\circ}} = \cos{96^{\circ} + 45^{\circ}} = \cos{141^{\circ}}.\] (Error compiling LaTeX. Unknown error_msg)
This means so
for some positive integer
(since the period of tangent is
), or
. Note that the inverse of
modulo
is itself as
, so multiplying this congruence by
on both sides gives
For the smallest possible
, we take
See Also
1996 AIME (Problems • Answer Key • Resources) | ||
Preceded by Problem 9 |
Followed by Problem 11 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
All AIME Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.