求证：2sin(π/4+a)sin(π/4-a)=cos2a

求证：2sin(π/4+a)sin(π/4-a)=cos2a 求证 cos（A）+ 根号3sin(A)=2sin(π/6+A) 当a∈(0,π/2)时,求证sin a 已知A+b+C=π 求证 cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) 若2sin(π/4+a）=sinθ+cosθ,2sin^2β=sin2θ,求证sin2a+(1/2)cos2β=0. 若2sin(π/4+a）=sinθ+cosθ,2sin^2β=sin2θ,求证sin2a+(1/2)cos2β=0 当a∈(0,π/2) 时 求证sinα 求证sin(3π/2-a)=-cosa 求证sin(3π/2+a)=-cosa 求证：sin(3/2π+a)=-cosa 求证:(sin 2x /(1-cos 2x) )·(sin x /(1+sin x))=tan (π/4-x/2). 求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 已知tanθ=(sin α-cos α)/(sin α+cos α) a,θ(0,π/2) 求证cos(3/2兀+ α) -sin(5π/2-α）=根号2sin(θ-4π） 求证sinx-cosx=根号2sin(x-π/4) 求证sin^4a+cos^4a=1-2sin^2acos^2a 化简:sin(-a)cos(2π+a)sin(-a-π) 求证数学题,在三角形ABC中,求证sin^2(A)+sin^2(B)+sin^2(C) 已知x+y=根号2sin(a+π/4),x-y=根号2sin(a-π/4),求证x^2+y^2=1