The witch of Agnesi curve is given by $y=\frac{125}{x^2+25}$. Determine the equation of the tangent line to the curve at $x=4$.

Evaluate the following derivative using the table given below.

$\frac{\text{d}}{\text{dx}}{\left(f\left(x\right)g\left(x\right)\right)}_{x=6}$

Evaluate the following derivative using the graph given below.

$\frac{\text{d}}{\text{dx}}{\left(xg\left(x\right)\right)}_{x=2}$

Calculate the derivative of the function $y=(4x-5)x^{\frac{1}{2}}$.