f(x)=5sin(Paix/3+@)+c=3设第一个正根是a1,则有第二个正根是a1+3即有f(a1)=5sin(Pai/3*a1+@)+c=3.................(1) f(a1+3)=5sin(Pai/3*(a1+3)+@)+c=3即有f(a1+3)=5sin(Pai/3a1+Pai+@)+c=-5sin(Pai/3a1+@)+c=3.............(2)(1)+(2)得2c=6c=3选择A吧.