From Patel 4U (Ex. 8B, Q5):
$A missile is fired from$\, O\, $with initial velocity$\, U\, $at an angle$\, \alpha\, $with the horizontal.$\\\\$ Prove that it describes a parabola of focal length$\,\frac{U^2\cos^2\alpha}{2g}\,.\\\\ $Also prove that any point$\, P(x,y)\, $within and on the...