分类：教育/科学-学习帮助
问题：高一数学怎么做已知sin(π/4
已知sin(π/4 -α)=5/13  ，求sin a/c(π/4+a) 的值。详细解答；非常感谢
回答：已知sin(π/4-α)=5/13 ，求sinα/cos(π/4+α)的值
解：已知sin(π/4-α)=5/13 ，==> cos(π/4-α)=±12/13. 又：
cos(π/4+α)
=sin[π/2-(π/4+α)]
=sin(π/4-α)=5/13
sinα
=sin[(π/4-α)+π/4]
=(√2/2)[sin(π/4-α)+cos(π/4-α)]
=(√2/2)[(5/13)±(12/13)]
=17√2/26或-7√2/26
所以
sinα/cos(π/4+α)=17√2/10 或-7√2/10