@Kitonum 
Thank you!

Also, I have another questions. Im graphing something given f(x)=2x^2-4x, i graph the functions:
f(x), 2f(x), 4f(x), -f(x), -2f(x), and -4f(x), using the domain -1<=x<=3. plot all graphs on the same x-y cord plane

f:=(x)-> 2x^2-4x: ## Function definition plot
({f(x),2f(x),4f(x),-f(x),-4*f(x)},x=0..5);

would this work to do the above? or should I include anything else?