## Algebra and Trigonometry 10th Edition

$h = \sqrt {d^2 - 3000^2}$, $d \geq 3000$
Use the Pythagarean theorem. $h^2 + 3000^2 = d^2$ $h = \sqrt {d^2 - 3000^2}$ Expression under the square root should be non-negative. $d^2 - 3000^2 \geq 0$ $d \geq 3000$