How can I plot a multivariable function?

syms x t r >> l=10; >> c=1500; >> w=1; >> z=(2/(r*c*pi))*(int(10*sin((r*pi*w)/l),0,l)*sin((r*c*pi*t)/l)); y=(2/l)*(int(sin((r*pi*w)/l),0,l))*cos((r*c*pi*t)/l); u(x,t)=symsum(sin((r*pi*x)/l)*(y+z),r,1,5)

u(x, t) =

sin((pi*x)/10)*((4*cos(150*pi*t))/pi + (4*sin(150*pi*t))/(15*pi^2)) + sin((pi*x)/5)*((4*cos(300*pi*t))/pi + (2*sin(300*pi*t))/(15*pi^2)) + sin((3*pi*x)/10)*((4*cos(450*pi*t))/pi + (4*sin(450*pi*t))/(45*pi^2)) + sin((2*pi*x)/5)*((4*cos(600*pi*t))/pi + sin(600*pi*t)/(15*pi^2)) + sin((pi*x)/2)*((4*cos(750*pi*t))/pi + (4*sin(750*pi*t))/(75*pi^2))

>> ezplot(u) >> x=0:20; >> ezplot(u) >> ezplot(u(x,t),x) Error using inlineeval (line 14)

I have been trying to plot the sum function u(x,t) and I want the graph axis to be u(x,t) and x. But I am having a problem. It only plots x and t but the results are not correct in this graph too.