当a∈(0,π/2)时,求证sin a

求证 cos（A）+ 根号3sin(A)=2sin(π/6+A) 求证：2sin(π/4+a)sin(π/4-a)=cos2a 求证数学题,在三角形ABC中,求证sin^2(A)+sin^2(B)+sin^2(C) 已知cos(a+B)+1=0,求证sin(2a+B)+sinB=0?(提示:sin(-a)=-sina). 求证：tan a/2＝(1-cos)/sin a=sin a/(cos a+1) 若2sin(π/4+a）=sinθ+cosθ,2sin^2β=sin2θ,求证sin2a+(1/2)cos2β=0 求当x趋近于a时,(sin x - sin a) /sin (x - a)的极限 求证sin^4a+cos^4a=1-2sin²acos²a 求证:sin a (1+cos2a)=sin a cos a 若cosA-2sin(A-B)=0,求证:tan(A-B)=cosB/(sinB+2) 已知cot(a+b)=0求证sin(a+2b)=sina 已知cos(a+b)=0,求证：sin(a+2b)=sina