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PracticalDragonfly2223

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Hello,

I don’t really understand what we should do in this question to find the answers can you explain this to me please?

Thank you in advance!

Louis-Philippe B

Thank you for your question!

For the two first questions, I recommend that you use some of the identities for cos(2t) and sin(2t). For example :

$$ cos(2t) = 2cos^2t-1 $$

$$ cos(2t) = 1 - 2sin^2t $$

$$ sin(2t) = 2sin(t)cos(t) $$

For the second part (with t/2), I recommend that you use the same formulas as above, but as equations. Specifically, you can consider cos(t) to be equivalent to cos(2•t/2), therefore, for example :

$$ -\frac{7}{9} = 2cos^2(\frac{t}{2})-1 $$

Don't hesitate to ask for more help if you need it!