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Find the exact value of cos2theta if sin2theta=3/4 and theta is between 0 and 90 degree

Sagot :

Answer :

[tex] \boxed{ \boxed{ \cos {}^{2} ( \theta) = \dfrac{1}{4} }}[/tex]

Solution :

According to a Trigonometric Identity :

[tex] \hookrightarrow \mathrm{\sin {}^{2} ( \theta) + \cos {}^{2} ( \theta) = 1}[/tex]

Now, let's solve for [tex] \cos²(\theta)[/tex]

[tex] \longrightarrow \dfrac{3}{4} + \cos {}^{2} ( \theta) = 1[/tex]

[tex] \longrightarrow \cos{}^{2}( \theta) = 1 - \dfrac{3}{4} [/tex]

[tex]\longrightarrow \cos {}^{2} ( \theta) = \dfrac{4 - 3}{4} [/tex]

[tex]\longrightarrow \cos {}^{2} ( \theta) = \dfrac{1}{4} [/tex]

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