Slope of line tangent to a curve at a given point, using First Principles Find, from first principles, the gradient of the tangent to the curve $y = 5 - x^2$ at the point $(1,4)$ on the curve.
So I'm currently lost on this question can some one please show me the solutions of how to complete this question and i may use it as an guide for future question. Thanks a lot!

$f`(x)= -2x$...(power rule, constant becomes zero)
point $(1,4)$, meaning $x=1$ and $y=4$
substitute $x=1$ in $f`(x)$ to obtain
$f`(1)= -2(1)=-2$ 
therefore slope of the tangent line is $m=-2$
$$y=mx+c$$
$$4=-2(1)+c$$
$$4= -2+c$$
$$4+2=c$$
$$c=6$$
$$y=-2x+6$$
