y=cosx-sinx
=√2(cosx*√2/2-sinx*√2/2)
=√2(cosx*cosπ/4-sinx*sinπ/4)
=√2(cosx*cosπ/4-sinx*sinπ/4)
=√2cos(x+π/4)
因为-1
余弦函数减正弦函数的最值
y=cosx-sinx
=√2(cosx*√2/2-sinx*√2/2)
=√2(cosx*cosπ/4-sinx*sinπ/4)
=√2(cosx*cosπ/4-sinx*sinπ/4)
=√2cos(x+π/4)
因为-1