证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40°

证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 如何证明sin(a+b)sin(a-b)=sin*a-sin*b (*为平方) 【证明】Sin A+sin B=2Sin 22 怎样证明/sin a +sin b/ 证明sina sin(a+2b) - sinb sin(b+2a) =sin(a+b)sin(a-b) 如何证明sin(a+b)=sin(a)cos(b)+cos(α)sin(b) 懂得进.证明,sina+sin(a+b)+sin(a+2b)+...sin(a+nb)=sin(a+ab/2)sin[(n+1)b/2]/sin(b/2) 证明sin(a+b)=sinacosb+cosasinb 证明sin(A+B)=sinAcosB+cosAsinB 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1 用正弦定理证明a+b/c=sin A+sin B/sin c 证明sin(A+B)sin(A-B)=cos^2B-cos^2A 证明 sin(A+B)cos(A-B)=sinAcosA+sinBcosB 证明三角函数等式sin(A+B)-sinA=2cos(A+B/2)sin(B/2) 证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40° 证明 SIN²A+SIN²B-SIN²C=2SINASINBCOSC cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明我 已经证明了sin(a+b)=sin(a)*cos(b)+cos(a)*sin(b) 用 三角形证明 了过程如下： 现在跪求希望大家帮我证明：cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 也用 三角形证明 . 如何证明sinA2-sinB2=sin(A-B)*sin(A+B)