sin(a-pia/4)=3/5,求sina

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/10/04 04:46:14

sin(a-π/4)=3/5
∴cos(a-π/4)=±4/5
（1）cos(a-π/4)=4/5
则sina
=sin[(a-π/4)+π/4]
=sin(a-π/4)*cos(π/4)+cos(a-π/4)sin(π/4)
=(3/5)*(√2/2)+(4/5)*(√2/2)
=7√2/10
（2）cos(a-π/4)=-4/5
则sina
=sin[(a-π/4)+π/4]
=sin(a-π/4)*cos(π/4)+cos(a-π/4)sin(π/4)
=(3/5)*(√2/2)+-(4/5)*(√2/2)
=-√2/10

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