α∈(π/2,π),且sinα=4/5,那么cosα=-3/5
sin(α+π/4)+cos(α+π)
=sinαcos π/4+cosαsinπ/4-cosα
=4/5*根号2/2-3/5*根号2/2-(-3/5)
=根号2/10+3/5
如果α∈(π/2,π),且sinα=4/5,那么sin(α+π/4)+cos(α+π)的值为?
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