QUESTION: Plot the function f(x) = cosx sin(2x) and its derivative, both on the same plot, for π ≤ x ≤ π . Plot the function with a solid line, and the derivative with a dashed line. Add a legend and label the axes. Okay, so this is what I have so far in a script file... x = [-pi: 0.01: pi]; y = cos(x)*sin(2*x); yd = 2*cos(x)*cos(2*x)-sin(x)*sin(2*x); plot (x,y,x,yd) But then I get this error: ??? Error using ==> mtimes Inner matrix dimensions must agree. Error in ==> p11 at 3 y = cos(x)*sin(2*x); I'm not worried about the details, that should be easy enough. (dotted/solid lines and legends and axes labeling.) I just want to make sure I can get it to plot. Also it asks to plot for π ≤ x ≤ π, but i have a feeling it means -π ≤ x ≤ π. It looks pretty simple, but I'm still learning this program and it's proving to be more difficult than it should be. Anyone have any ideas what's wrong with my script? Thanks!