已知sin(a+π/12)=1/3,则cos(a+7π/12)的值等于

已知A,B,C∈(0,π) 若有A+B+C=π,试证：sin(2/A)+sin(B/2)+sin(C/2)≤3/2 已知sin(π/12-a)=1/3,且-π 已知sin(π+a)=1/3,则sina= 已知 sin a-cos a=1/2,则 sin^3 a-cos^3 a 已知A+b+C=π 求证 cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) 已知sin(a+π/4)+sin(a-π/4)=√2/3则sin(a-π/4)/1-cos2a-sin2a的值 已知sin(π/6-a)=根号3/3,则sin(5π/6+a)= 已知sin(a+π/4)sin(a-π/4)=1/3,若π/2 已知sin(3π-a)=-2sin(π/2+a)则sinacosa等于 3 在三角形ABC中,已知（a2+b2）sin（A-B）=（a2-b2）sin(A+B) 求证：ABC是等腰或直角三角形(a^2+b^2)sin(A-B)=(a^2-b^2)sin(A+B),(sin^A+sin^B)sin(A-B)=(sin^A-sin^B)sin(A+B) sin^A*(sin(A+B)-sin(A-B))=sin^B*(sin(A-B)+sin(A+B)) sin^A*2c 已知sin(a+x)=1/2,sin(a-x)=1/3,则tana/tanx 已知 sinα + cosα / sinα - cosα = 2 ,则 sin(α-5π) x sin(3π/2-α)等于A,3/4B,±3/10C,3/10D,-3/10 △ABC中,已知sin²A=sin²B+sinBsinC+sin²C,则A等于 三角形ABC中,已知（sin^2 A-sin^2 B-sin^2 C)/(sinB sinC)=1 求A? 已知角a为钝角,且sin(a+π/12)=1/3,则cos(a+5π/12)=? 已知在△ABC中,cosA=2√2/3,求[2sin(A+π/4)sin(B+C+π/4)]/(1-cos2A)的值 极坐标系中,已知一个圆的方程为ρ=12sin(θ-π/6）,则过圆心且和极轴垂直的直线的极坐标方程为A.ρsinθ=3√3 B.ρsinθ-3√3 C.ρsinθ=-3 D.ρsinθ=3 已知sin(π/2-x)+sin(π-x)/cos(-x)+sin(2π-x)=2009,则tan(x+5π/4)等于?已知sin(π/2-x)+sin(π-x)/cos(-x)+sin(2π-x)=2009,则tan(x+5π/4)等于（） A.-2009 B.-1/2009 C.1/2009 D.2009