cos(-19π/4)的值
问题描述：
cos(-19π/4)的值
答
cos(-19π/4)
=cos(19π/4)
=cos(19π/4-4π)
=cos(3π/4)
=cos(π/2+π/4)
=-sinπ/4
=-√2/2.
答
cos(－19π/4)
=cos(19π/4)
=cos[4π＋3π/4]
=cos(3π/4)
=cos[π－π/4]
=－cos(π/4)
=－√2/2