cosx=1/3,cos(x+y)=-3/5,且x,y都是锐角,则cosy=,
问题描述:
cosx=1/3,cos(x+y)=-3/5,且x,y都是锐角,则cosy=,
答
x是锐角
sinx>0
sin²x+cos²x=1
sinx=2√2/3
0
所以sin(x+y)=4/5
cosy=cos[(x+y)-x]
=cos(x+y)cosy+sin(x+y)siny
=(8√2-3)/15