Question 78583
720/(S-30)+720/(S+30)=10
[720(S+30)+720(S-30)]/(S-30)(S+30)=10
(720S+21600+720S-21600)/(S^2-900)=10 COMBINE TERMS & CROSS MULTIPLY
1440S=10S^2-9000
10S^2-1440S-9000=0
S^2-144S-900=0 NOW FACTOR:
(X-150)(X+6)=0
X-150=0
X=150 ANSWER FOR THE SPEED OF THE PLANE IN STILL AIR.
PROOF
720/120+720/180=10
6+4=10
10=10