设sin(π/4+α)+cos(π/4+α)=-1/5,则cos2α=

设sin(π/4+α)+cos(π/4+α)=-1/5,则cos2α= 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题设a为锐角,证：1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)2、cos a-sin a=根号2cos(4分之π+a) 设α∈（0,π/2）,则cosα,sin(cosα),cos(sinα)的大小关系为什么? 利用和差角公式化简 (2)sin(π/3+α)+sin(π/3-α)(2)sin(π/3+α)+sin(π/3-α)(3)cos(π/4+α)-cos(π/4-α)(4)cos(60°+α)+cos(60°-α)(5)sin(α-β)cosβ+cos(α-β)sinβ(6)cos(α+β)cosβ+sin(α+β)sinβ cos^2(π/4+α)=(cos(π/4)cosα-sin(π/4)sinα)² cos^2(π/4+α)是怎么等于(cos(π/4)cosα-sin(π/4)sinα)²的? 设sin2α=1/4,α∈（π/4,π/2）,求 cosα-sinα的值 设α∈(0,π/2),若sinα=4/5,则cos(α-π/3)等于? 设α为锐角,若cos(α+π/6)=4/5,求sin（2α+π/12）, 设α属于(0,π/2),若sinα=3/5,则√2cos(α+π/4)等于 设α∈（0,π/4),且sin2α=1/4,则cosα-sinα的值是 设5π＜θ＜6π,cosθ∕2﹦α则sinα∕4＝? 设α∈(0,π/4),sinα+cosα=7/5,则tanα=___ 设sin(π/4-x)=5/13,则cos2x/cos(π/4+x)=_______ 设sin(π/4-x)=5/13,则cos2x/cos(π/4-x)=_______ 设sin(π/4-a/2)cos(π/4-a/2)=1/6,求sin2a 设f(cos^2x)=sin^2x,则f'(π/4)等于, 设a为常数,解方程cos(x-π/4)=sin(2x)+a 化简sin(π/4+α)cosα-sin(π/4-α)sinα