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Help me please i want to see if i did it correctly

Help me please i want to see if i did it correctly-example-1
User Ivagarz
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1 Answer

21 votes
21 votes

-1/16

1) Considering that we have the following identity:


\begin{gathered} \cos (2x)=2\cos (2x)-1 \\ \end{gathered}

2) We can plug into that the cos (x).:


\begin{gathered} \cos (2x)=(\frac{\sqrt[]{15}}{4})^2-1 \\ \cos (2x)=(15)/(16)-(16)/(15) \\ \cos (2x)=-(1)/(16) \end{gathered}

Since for the Quadrant II cosine yields a negative value.

User Dscher
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