已知cosx-sinx=325,则5sin2x/cos(x+π4)=_.
问题描述:
已知cosx-sinx=
,则3
2
5
=______. 5sin2x cos(x+
)π 4
答
∵cosx-sinx=
,3
2
5
∴两边平方,可得1-sin2x=
18 25
∴sin2x=
7 25
又由cos(x+
)=π 4
(cosx-sinx)=
2
2
×
2
2
=3
2
5
,3 5
则
=5sin2x cos(x+
)π 4
=5×
7 25
3 5
.7 3
故答案为:
.7 3