Sebelumnya oerlu diingat bahwa
cos (-a) = cos a.
Sehingga,
cos (-75) = cos 75
cos 75 = cos (30+45)
= cos 30.cos 45 - sin 30.sin 45
= ½√3 . ½√2 - ½ . ½√2
= ¼√6 - ¼√2
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Sebelumnya oerlu diingat bahwa
cos (-a) = cos a.
Sehingga,
cos (-75) = cos 75
cos 75 = cos (30+45)
= cos 30.cos 45 - sin 30.sin 45
= ½√3 . ½√2 - ½ . ½√2
= ¼√6 - ¼√2