How to graph the tangent to a curve at some point?

[Juwane]

Using a graphing software, I'm trying to graph three things:

1. The function x^2.
2. It's derivative 2x.
3. The tangent to the curve at point 3.

Now I know that that if I want to find the slope of the curve at point 3, I should substitute 3 into the derivative 2x, which will give 6. What I want is the tangent line, not it's slope, at point 3. What equation should I input into the software to show the tangent to the curve at point 3? Please help.

 

[Bohrok]

Asking the program to get the line tangent to a point on the graph probably depends on the program.
Why not use the equation for a tangent line at point (a, f(a))
y = f'(a)(x - a) + f(a)

 

[Juwane]

Asking the program to get the line tangent to a point on the graph probably depends on the program.
Why not use the equation for a tangent line at point (a, f(a))
y = f'(a)(x - a) + f(a)

It worked! How did you derive this equation?

EDIT: Never mind, I've find out.