化简 (sin π/4 cos x)ˆ2-(cos π/4 sin x)ˆ2
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化简 (sin π/4 cos x)ˆ2-(cos π/4 sin x)ˆ2
化简sin(π/4+x)sin(π/4-x)
展开后化成这步骤,下步怎么化
化简sin(π/4+x)sin(π/4-x)
展开后化成这步骤,下步怎么化
利用诱导公式:sin(π/2-a)=cosa ,sin(π/2+a)=cosa 即可.
sin(π/4+x)sin(π/4-x)
=sin(π/4+x)sin[π/2-(π/4+x)]
=sin(π/4+x)cos(π/4+x)
=1/2sin[2(π/4+x)]
=1/2sin(π/2+2x)
=1/2cos2x
=(cosx)^2-1/2.
诱导公式很重要,一定要熟练.
而积化和差公式可记可不记.
sin(π/4+x)sin(π/4-x)
=sin(π/4+x)sin[π/2-(π/4+x)]
=sin(π/4+x)cos(π/4+x)
=1/2sin[2(π/4+x)]
=1/2sin(π/2+2x)
=1/2cos2x
=(cosx)^2-1/2.
诱导公式很重要,一定要熟练.
而积化和差公式可记可不记.
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