Looking for a function calculator

Question

I am looking for a calculator which can calculate functions like $f(x) = x+2$ at $x=a$ etc; but I am unable to do so. Can you recommend any online calculator?

Answer 1

Try the Desmos Graphing Calculator. The output looks really nice.

See an interactive example of drawing lines.

Answer 2

GeoGebra works well for this, eg http://web.geogebra.org/?command=f(x)=x+2;a=2;f(a)