Here is how I plotted the assignment using Maple (available in the EECE Computer pod). 

Here is the Maple code in case it is a little hard to read in the pictures above.  I usually use a text editor (Word) to type up the code at home and then go to the eece pod to actually run it.

with (plots):
v1 := ((20/(evalf(Pi))) * cos(2*t)) - ((20/(3*evalf(Pi))) * cos(6*t)) + ((20/(5*evalf(Pi))) * cos(10*t));
v1plot := plot(v1(t), t=-5..5, y=-7..7):
display ({v1plot});

i1 := (3.95 * cos((2*t) + (convert(29.7*degrees,radians)))) + (1.92 * cos((6*t) - (convert (162.9*degrees, radians)))) + 1.23 * cos((10*t) - (convert(10.9*degrees,radians))));
v2plot := plot(v2(t), t=-5..5, y=-7..7):
display ({v2plot});

A couple of places where I normally make mistakes:
For degrees always put a decimal point 128.7 instead of 129  After you put in your line of code (v1 := .....) and hit return, take a minute to do a little mental calculation to make sure the value mirrored back to you seems correct since it is easy to put a ( in the wrong place. 

If you want to do an exponential,  it is:  exp(.....)