Equation of a tangent line

I'm having a little trouble in my cal class and I'm trying to see if i can get some help. not really wanting the answer just some clarification on a problem.

the question is

- Find the equation of the line tangent to the graph of f(x)= x^1/2 at x=4. Express answer in "y=mx+b" form. Use fractions, not decimals. do NOT use the limit definition of derivative.

My question is what definition can i use thats not the limit definition?? i haven't figured out what she means yet...

Re: Equation of a tangent line

i.e. use the power rule to get the derivative.