求证:(sinα+sinβ)/sin(α+β)=cos((α-β)/2)/cos((α+β)/2)
若0<α<β<π/4,sinα+cosα=a,sinβ+cosβ=b,则【 】
若α∈(0,π/2),tan2α=cosα/(2-sinα),则tanα=【 】
若 sinx = −2/3, 则 cos2x = _______.
已知 sinθ + sin(θ + π/3) = 1, 则 sin(θ + π/6) =【 】
已知 tanθ = 2, 则 cos2θ = _______, tan(θ − π/4) = _______.
已知sin2(π/4+α)=2/3, 则sin2α的值是_______.
已知0<x<π/2,简化: lg(cosx•tanx+1-2sin2(x/2))+lg[cos( x-π/4)]-lg( 1+sin2 x).