以知sin阿而法等于负五分之三,阿而法属于(二分之三派,二派) 求cos(阿而法+四分之派)的值.

sinα=-3/5，α∈((3π)/2，2π)
α=arc sin(-3/5)=5.639684弧度=1.795167*π弧度
cos(α+π/4)
=cos(1.795167*π+π/4)
=cos(2.045167*π)
=cos(2π+0.045167*π)
=cos(0.045167*π)
=0.99898

sinα=-3/5,α∈（3π/2,2π）
则cosα=√(1-sin²α）=4/5
cos(α+π/4）=cosα cosπ/4-sinα sinπ/4
=4/5×√2/2-(-3/5)×√2/2
=(4/5+3/5)×√2/2
=8/5×√2/2
=4√2/5