To find the distance between two points, we use the distance formula:

$d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$

Given points: $(4,0)$ and $(2,-9)$, where $(x_1, y_1) = (4, 0)$ and $(x_2, y_2) = (2, -9)$.

Substitute the values into the formula:

$d = \sqrt{(2 - 4)^2 + (-9 - 0)^2}$

Simplify the expression:

$d = \sqrt{(-2)^2 + (-9)^2}$ $d = \sqrt{4 + 81}$ $d = \sqrt{85}$

So, the distance between the two points in simplest radical form is $\sqrt{85}$.

Would you like any further details or explanations?

Here are some related questions you might find helpful:

1. How do you calculate the midpoint between two points?
2. What is the equation of a line passing through two points?
3. How do you convert the distance formula into slope-intercept form?
4. How can you find the distance between two points on a 3D plane?
5. How can you verify if two points lie on the same circle?

Tip: Remember, the distance formula is derived from the Pythagorean theorem applied to the differences in coordinates!