sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b

证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20° 【证明】Sin A+sin B=2Sin 22 证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 并利用该式计算sin^2 20度=sin 80度 求sin²20°+sin80°sin40°,并且要用sin(α+β)sin(α-β)=sin²α-s 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 sin^2 (A)+sin^2(B)-sin^2(A)sin^2(B)+cos^2(A)cos^2(B) sin^2A+sin^2B=sin^2C求证△ABC的形状 在三角形ABC中,sin*2A+sin*2B=sin*2C 在三角形ABC中sin^A+sin^B=2sin^C,则角C为? 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2 1:sin(a-b)=sin(-b+a)