Question 1202670
Imagine  the two planes are moving  towards P

The two places are at right angles to each other. ( In same Plane)


Form  two equations that shows  the  position  of each plane.

Plane A position at any time = 150 - 450t

Place B position = 200 - 450t  perpendicular 

The d istance between tem  will be  hypotenuse of the triangle with sides that are given   by Plane A & B positions

c^2= a^2 + b^2 (Pythagoras Theorem)


c(t)^2 = (150t- 450)^2 +(200t-450)^2

22500t2-135000202500 +40000t^2-180000+202500

simplify to get the required function