f(x+pai/6)=Asin(2x+pai/3+a)=Acos(pai/6-a-2x)
pai/6-a=2kpai,pai/6-a=2kpai+pai
f(x)=Asin(2x+pai/6-2kpai)=Asin(2x+pai/6)
f(pai/6)=Asinpai/2=A=4
a=-7/6pai-2kpai
f(x)=Asin(2x-7/6pai)
f(pai/6)=Asin(-5/6pai)=-A/2=4
A=-8
f(x)=4sin(2x+pai/6)