Question

Determine the value of \cos^2 15\degree -\dfrac{1}{2}

Collected in the board: Trigonometry

Steven Zheng posted 5 months ago

Answer

Using the double angle identity

\cos 30\degree =2\cos^2 15\degree -1

Divide both sides with 2, we get

\cos^2 15\degree -\dfrac{1}{2} =\dfrac{1}{2} \cos 30\degree =\dfrac{\sqrt{3} }{4}


Steven Zheng posted 4 months ago

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