Answer:
The tangent line to the given curve at the given point is
.
Step-by-step explanation:
To find the slope of the tangent line we to compute the derivative of
and then evaluate it for
.
Differentiate the equation.
Differentiate both sides.
Sum/Difference rule applied: 
Constant multiple rule applied: 
Applied power rule: 
Simplifying and apply constant rule: 
Simplify.
Evaluate y' for x=4:


is the slope of the tangent line.
Point slope form of a line is:

where
is the slope and
is a point on the line.
Insert 9 for
and (4,10) for
:

The intended form is
which means we are going need to distribute and solve for
.
Distribute:

Add 10 on both sides:

The tangent line to the given curve at the given point is
.
------------Formal Definition of Derivative----------------
The following limit will give us the derivative of the function
at
(the slope of the tangent line at
):

We are given f(4)=10.

Let's see if we can factor the top so we can cancel a pair of common factors from top and bottom to get rid of the x-4 on bottom:

Let's check this with FOIL:
First: 
Outer: 
Inner: 
Last: 
---------------------------------Add!

So the numerator and the denominator do contain a common factor.
This means we have this so far in the simplifying of the above limit:



Now we get to replace x with 4 since we have no division by 0 to worry about:
2(4)+1=8+1=9.