Algebra Vs. Calculus

1. The difference between f(c) and f(x) x->c ...
When your finding the limit as x approaches c, your output is getting closer and closer to that constant, but when you plug in c, you automatically get an output.

2.Simmilarities between slope of a line, and derivative...
To find the slope of a line, you need the change of y/x, and to find the derivative, the first step is finding the slope, so they somewhat need each other.

Limits?

I understand limits, for the most part
these are some problems I'm still not sure about

1) lim 3 sin4x/sin3x
x->0

2) lim sinx/2x^2-x
x->0

3)lim sin^2x/x
x->0

Would appreciate help, thanks