解析：∵f(x)=sin(wx+fai)(w>0,-π≤faiT=5π/2==>w=4/5
∴f(x)=sin(4/5x+fai)
f(3π/4)=sin(3π/5+fai)=-1==>3π/5+fai=3π/2==>fai=9π/10
∴fai=9π/10,f(x)=sin(4/5x+9π/10)