Let $f(x) = \sqrt{4225 - x^2}$.
Then the slope of the tangent line to the graph of $y=f(x)$ at the point $(33,56)$
is the limit as $x$ tends to of the following expression .

To simplify this expression, we multiply numerator and denominator by
.

The value of this limit is .

It follows that the equation of the tangent line is $y =$ .