Difference between revisions of "2021 AMC 12B Problems/Problem 13"
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==Problem== | ==Problem== | ||
− | How many values of <math>\theta</math> in the interval <math>0<\theta\le 2\pi</math> satisfy< | + | How many values of <math>\theta</math> in the interval <math>0<\theta\le 2\pi</math> satisfy<math></math>1-3\sin\theta+5\cos3\theta = 0?<math> |
+ | </math><math>\textbf{(A) }2 \qquad \textbf{(B) }4 \qquad \textbf{(C) }5\qquad \textbf{(D) }6 \qquad \textbf{(E) }8</math> | ||
==Solution== | ==Solution== |
Revision as of 16:56, 20 December 2022
Contents
[hide]Problem
How many values of in the interval satisfy$$ (Error compiling LaTeX. Unknown error_msg)1-3\sin\theta+5\cos3\theta = 0?$$ (Error compiling LaTeX. Unknown error_msg)
Solution
We rearrange to get We can graph two functions in this case: and . Using transformation of functions, we know that is just a cosine function with amplitude and period . Similarly, is just a sine function with amplitude and shifted unit downward: So, we have solutions.
~Jamess2022 (burntTacos)
Video Solution (quick, no graphing)
https://youtu.be/YTn5YPQt6IY ~ MathProblemSolvingSkills.com
Video Solution by OmegaLearn (Using Sine and Cosine Graph)
~ pi_is_3.14
Video Solution by Hawk Math
https://www.youtube.com/watch?v=p4iCAZRUESs
See Also
2021 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 12 |
Followed by Problem 14 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.