nilai dari cos165°=
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[tex] \cos( {165}^{o} ) [/tex] [tex] = \cos( {30}^{o} + {135}^{o} ) [/tex]
[tex] = \cos( {30}^{o}) \times \cos( {135}^{o} ) - \sin( {30}^{o} ) \times \sin( {135}^{o} ) [/tex]
[tex] = \frac{1}{2} \sqrt{3} \times ( - \frac{1}{2} \sqrt{2} ) - \frac{1}{2} \times \frac{1}{2} \sqrt{2} [/tex]
[tex] = - \frac{1}{4} \sqrt{6} - \frac{1}{4} \sqrt{2} [/tex]
[tex] = - \frac{1}{4} ( \sqrt{6} + \sqrt{2} )[/tex]
[answer.2.content]
