作业帮3.4.5.题
来源：学生作业帮 编辑：作业帮 分类：数学作业 时间：2024/05/28 02:37:43
3.4.5.题
3)cos(a-b)=√5/5,cos2a=√10/10
sin(a-b)=-2√5/5,sin2a=3√10/10
cos(a+b)=cos[2a-(a-b)]=cos(a-b)cos2a+sin(a-b)sin2a
=√5/5*√10/10-2√5/5*3√10/10
=-√2/2
a+b=3π/4
4)原式＝sin(60+60)=sin120=√3/2
5)cosa+√3sina=2(1/2cosa+√3/2sina)=2sin(a+π/6)
=2sin[π/2-(π/3-a)]=2cos(π/3-a)=2*1/8=1/4
sin(a-b)=-2√5/5,sin2a=3√10/10
cos(a+b)=cos[2a-(a-b)]=cos(a-b)cos2a+sin(a-b)sin2a
=√5/5*√10/10-2√5/5*3√10/10
=-√2/2
a+b=3π/4
4)原式＝sin(60+60)=sin120=√3/2
5)cosa+√3sina=2(1/2cosa+√3/2sina)=2sin(a+π/6)
=2sin[π/2-(π/3-a)]=2cos(π/3-a)=2*1/8=1/4