Calculus
posted by Samuel .
At noon, ship A is 20 nautical miles due west of ship B. Ship A is sailing west at 23 knots and ship B is sailing north at 17 knots. How fast (in knots) is the distance between the ships changing at 5 PM? (Note: 1 knot is a speed of 1 nautical mile per hour.)

draw the diagram.
I see this
d= sqrt(ND^2+(WD+20)^2) where ND is north distance, WD is west distance
take the derivative
d'= 1/2 *1/(sqrt( ) * 2ND*ND'+2(WD+20)(WD')
ND= 17kt/hr*5hrs ND'=17kts/hr
WD=23*5 WD'=23
have fun. 
what do you mean by 1/(sqrt()?

what do you mean by 1/(sqrt()?