求sin18°×sin54°的详细解答过程,
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求sin18°×sin54°的详细解答过程,
sin18sin54=[cos(-36)-cos72]/2
=(cos36-cos72)/2
=(2sin36cos36-2sin36cos72)/4sin36
=[sin72-sin108-sin(-36)]/4sin36
=(sin72-sin72+sin36)/4sin36
=1/4
=(cos36-cos72)/2
=(2sin36cos36-2sin36cos72)/4sin36
=[sin72-sin108-sin(-36)]/4sin36
=(sin72-sin72+sin36)/4sin36
=1/4