sinx+siny=2sin[(a+b)/2]cos[(a-b)/2]sinx-siny=cosx+cosy=cosx-cosy=sinxcosy=cosxsiny=cosxcosy=sinxsiny=

已知cosa=cosx*siny,cosb=sinx*siny求证：sin^2a+sin^2b+sin^2y=2 sinx+siny=2sin[(a+b)/2]cos[(a-b)/2]sinx-siny=cosx+cosy=cosx-cosy=sinxcosy=cosxsiny=cosxcosy=sinxsiny= 三角函数题目：已知：cosa=cosx*siny cosb=sinx*siny 求证：sin^2*a+sin^2*b+sin^2*ysin^2*a+sin^2*b+sin^2*y 应该是 sin^2a+sin^2b+sin^2y =2 一道简单的三角比证明题求证：4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)sin2x(cos2y-1)+sin2y(cos2x-1) =-2sin2x(siny)^2-2sin2y(sinx)^2有一个负号啊~但是另一边化简出来没有负号，难道cos2y=2(siny)^2+ 证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx 求证sin（2x+y)/sinx-2cos(x+y)=siny/sinx 证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2 求证：sin(2x+y)/sinx-2cos(x+y)=siny/sinx 证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2. 证明sin(x+y)sin(x-y)=sinx-siny 已知sinx+siny=2/3,求2/3+siny-cos²a取值范围 已知sinx+siny=2/3,求2/3+siny-cos²a取值范围 arcsin(sinx+siny)+arc(sinx-siny)=kπ/2,K为奇数,求sin^2x+sin^2y的值 (a)证明cos(x-y)-cos(x+y)=2*sinx*siny (b)由此,证明 2sinθ(sinθ+sin3θ+sin5θ+sin7θ)=1-cos 8θ 已知sinx减siny等于负三分之二（sinx-siny=-2/3）；cosx加cosy等于三分之二（cosx+cosy=2/3）且x,y为锐角则sin(x+y)的值为A:1 B:-1 C:1/3 D:1/2 看清题 cosx-cosy=1/2,sinx-siny=1/3,sin(x+y)=RT sinx-siny=1/3,cosx-cosy=2/3,sin(x+y)=? 请问,如何证明sinx+siny=2*sin(x+y/2)*cos(x-y/2)