arcsinx的值域是[-π/2,π/2]
arccosx的值域是[0,π]
arcsin(sin3π/4)+arccos(cos3π/4)
由诱导公式
=arcsin(sin(π-3π/4))+3π/4
=arcsin(sin(π/4))+3π/4
=π/4+3π/4
=π