clearx=pi.pi;y=sin(x);y=cos(x);y=tan(x);plot(x，y，’r’，x，y，’g’，x，y，’b’);clearx=pi.pi;y=sin(x);plot(x，y，’r’)holdony=cos(x);plot(x，y，’g’)y=tan(x);plot(x，y，’b’)