Question

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Answer 1

$cos^{2} \alpha = 1 - {sin}^{2} \alpha = 1 - {0.75}^{2} = 1 - {( \frac{3}{4}) }^{2} = 1 - \frac{9}{16} = \frac{16}{16} - \frac{9}{16} = \frac{7}{16} \\ cos \alpha = + - \frac{ \sqrt{7} }{4}$