Hello, I'm required to use the definition:

m = lim as x approaches a of (f(x)-f(a))/(x-a)

to find the slope of the tangent line of the function: y=4x-x^2 at the point (1,3).

So I now have:

lim x->1 [(4x-x^2)-f(1)]/(x-1) which comes out to

lim x->1 (4x-x^2-3)/(x-1).

I still have 0 in the denominator for direct substitution so I thought about multiplying by the conjugate x+1 but that would still give me x^2-1 which would still be 0. Any thoughts on how to continue this problem?

Thanks.