ACT 2019 April(Z15) Math Question 14 Explanation - ACT Helper

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2019 April(Z15) Math Question 14
Trigonometry
- Pythagorean Theorem & sin cos tan
Choice H
$\sin^{2} (θ) + \cos^{2} (θ) = 1$ $\Rightarrow \sin^{2} (α) + \cos^{2} (α) = 1$ $\Rightarrow (\frac{15}{17})^{2} + \cos^{2} (α) = 1$ $\Rightarrow \frac{225}{289} + \cos^{2} (α) = 1$ $\Rightarrow \cos^{2} (α) = \frac{64}{289}$ $\Rightarrow \cos (α) = \sqrt{\frac{64}{289}} = \frac{8}{17}$
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