三角函数的转换问题!y=sina【2(x+π/4)+π/3】=cos(2x+π/3)这是怎么转换的)急!

解
y=sin[2(x+π/4)+π/3]
=sin(2x+π/2+π/3)
=sin[π/2+(2x+π/3)]
=sinπ/2cos(2x+π/3)+cosπ/2sin(2x+π/2)
=cos(2x+π/3)
其实是有一条公式的
sin[π/2+a)=cosa
∴上面那步sin[π/2+(2x+π/3)]直接等于cos(2x+π/3)