sin12*sin48*sin54=?
展开全部
sin54-sin18
=2sin18cos36
=2sin18cos18cos36/cos18
=1/2sin72/cos18
=1/2
sin12*sin48*sin54
=(cos36-cos60)/2 *sin54
=[(cos36-cos60) *sin54]/2
= [(sin90+sin18)/2-(sin54)/2]/2
= 1/4+ (sin18)/4-(sin54)/4
= 1/4 -（sin54-sin18）/4
= 1/4-1/8
= 1/8
=2sin18cos36
=2sin18cos18cos36/cos18
=1/2sin72/cos18
=1/2
sin12*sin48*sin54
=(cos36-cos60)/2 *sin54
=[(cos36-cos60) *sin54]/2
= [(sin90+sin18)/2-(sin54)/2]/2
= 1/4+ (sin18)/4-(sin54)/4
= 1/4 -（sin54-sin18）/4
= 1/4-1/8
= 1/8
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