已知函数y=Asin(ωx+φ)(A>0,ω>0,|φ|0,ω>0,|φ|T=4π==>w=2π/T=1/2==>f(x)=3sin(1/2x+φ)
又它与y轴的交点为(0,3/2),
∴f(0)=3sin(φ)=3/2==>φ=π/6
∴f(x)=3sin(1/2x+π/6)
(2) y=sinx==>y=3sin(1/2x+π/6)
*将坐标系纵坐标扩大3倍,横坐标不变得y=3sinx
**将y=3sinx图像左移π/6个单位,得y=3sin(x+π/6)
***将坐标系横坐标扩大到原来的2倍,纵坐标不变得y=3sin(1/2x+π/6)
(3)解析：
单调递增区间：2kπ-π/2