因为sinx=-15/17 x属于(3π/2,2 π)
所以cosx=8/17
sin(x+π/4) cos(π/4- x)
=(sinxcosπ/4+cosxsinπ/4)(cosπ/4cosx+sinπ/4sinx)
=[(√2/2)(sinx+cosx)][(√2/2)(sinx+cosx)]
=(8/17-15/17)²/2
=49/578
因为sinx=-15/17 x属于(3π/2,2 π)
所以cosx=8/17
sin(x+π/4) cos(π/4- x)
=(sinxcosπ/4+cosxsinπ/4)(cosπ/4cosx+sinπ/4sinx)
=[(√2/2)(sinx+cosx)][(√2/2)(sinx+cosx)]
=(8/17-15/17)²/2
=49/578