Question

If x is an integer in the first quadrant and sin(x)=3/4 find sin(2x), cos(2x), and tan(2x)

Answer 1

Answer:

$\sin(x) = \frac{ 3}{4} \\ {sin}^{2}(x) + {cos}^{2}(x) = 1 \\ {cos}^{2}(x) + {( \frac{3}{4} )}^{2} = 1 \\ {cos}^{2}(x) = 1 - \frac{9}{16} = \frac{7}{16} \\ cos(x) = \frac{ \sqrt{7} }{4} \\or \\ {4}^{2} - {3}^{2} = {a}^{2} \rightarrow {a}^{2} = 16 - 9 = 7 \\ a = \sqrt{7} \\ cos(x) = \frac{ \sqrt{7}}{4} \\ \tan(x) = \frac{ \sin(x) }{ \cos(x) } = \frac{ \frac{3}{4} }{ \frac{ \sqrt{7} }{4} } = \frac{3}{ \sqrt{7} } \\ \sin(2x) = 2 \sin(x) \cos(x) \\ = 2( \frac{3}{4} . \frac{ \sqrt{7} }{4} ) \\ \sin(2x) = \frac{3 \sqrt{7} }{8} \\ \cos(2x) = { \cos(x) }^{2} - { \sin(x) }^{2} \\ = 1 - 2 { \sin(x) }^{2} \\ \tan(2x) = \frac{ \sin(2x) }{ \cos(2x) }$