三角比证明题证明:1)(√3/2)×sinx + (1/2)×cosx = sin(x+π/6)2) sin(α+β)+
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三角比证明题
证明:1)(√3/2)×sinx + (1/2)×cosx = sin(x+π/6)
2) sin(α+β)+ sin(α-β) = 2sinαcosβ
3) sin[(5π/6)-α]+sin[ (5π/6)+α] = cosα
证明:1)(√3/2)×sinx + (1/2)×cosx = sin(x+π/6)
2) sin(α+β)+ sin(α-β) = 2sinαcosβ
3) sin[(5π/6)-α]+sin[ (5π/6)+α] = cosα
原式左边可变为
cosπ/6×sinx+sinπ/6×cosx
=sin(x+π/6)证毕
2)sin(α+β)+ sin(α-β) =sina*cosβ+cosa*sinβ+sina*cosβ-cosa*sinβ=2sinαcosβ
3)sin[(5π/6)-α]+sin[ (5π/6)+α]
=sin(5π/6)*cosa-cos(5π/6)*sina +sin(5π/6)*cosa+cos(5π/6)*sina
=2sin(5π/6)*cosa
=2sin(2π-π/6)*cosx
=2sin(π/6)*cosa
=2*(1/2)*cosa
=cosa
cosπ/6×sinx+sinπ/6×cosx
=sin(x+π/6)证毕
2)sin(α+β)+ sin(α-β) =sina*cosβ+cosa*sinβ+sina*cosβ-cosa*sinβ=2sinαcosβ
3)sin[(5π/6)-α]+sin[ (5π/6)+α]
=sin(5π/6)*cosa-cos(5π/6)*sina +sin(5π/6)*cosa+cos(5π/6)*sina
=2sin(5π/6)*cosa
=2sin(2π-π/6)*cosx
=2sin(π/6)*cosa
=2*(1/2)*cosa
=cosa
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