若0
来源：学生作业帮助网 编辑：六六作业网 时间：2024/12/19 16:45:35
若0若0若0cos(x+y/2)=cos[(x+π/4)-(π/4-y/2)]=cos(x+π/4)cos(π/4-y/2)+sin(x+π/4)sin(π/4-y/2)cos数值都知道了,sin(x
若0 若0
若0
cos(x + y/2) = cos [(x + π/4) - (π/4 - y/2)]
= cos (x + π/4) cos (π/4 - y/2) + sin (x + π/4) sin ( π/4 - y/2 )
cos数值都知道了,
sin (x+π/4) = sqrt [ 1-(cos(x+π/4))^2 ] = 2sqrt(2) / 3；
sin (π/4 - y/2) = sqrt [ 1-(cos(π/4 - y/2))^2 ] = sqrt(6) / 3；
注意在上面求sin的时候注意检查下x+π/4和π/4 - y/2的范围,看是否落在sin取正的区间.
最后,cos (x + y/2) = 5sqrt(3)/9.