calculer cos²6 - cos²24 = 1/8(√5 -1) sin²39 - sin²24 = 1/8(√15 -(√3)
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Question
calculer cos²6 - cos²24 = 1/8(√5 -1)
sin²39 - sin²24 = 1/8(√15 -(√3)
1 Réponse
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1. Réponse Anonyme
calculer
cos²6 - cos²24
=(cos(6)+cos(24))(cos(6)-cos(24))
=2cos(18)cos(30) * -2sin(18)sin(30)
=-sin(36)sin(60)
=-1/8(1-√5)
=1/8(√5-1)
sin²39 - sin²24
=(sin(39)-sin(24))(sin(39)+sin(24))
=2cos(31,5)sin(7,5) * 2cos(7,5)sin(31,5)
=-sin(63)sin(15)
=-1/8(√3-√15)
=1/8(√15-√3)