SOLUTION: You and your friend part at an intersection. You drive off north at a constant speed, and your friend drives east at a speed that is 9 mph higher. After 3 hours the distance betwee

Question 898767: You and your friend part at an intersection. You drive off north at a constant speed, and your friend drives east at a speed that is 9 mph higher. After 3 hours the distance between you and your friend is 282.78 miles. You have been driving at _______ mph.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
You and your friend part at an intersection.
You drive off north at a constant speed, and your friend drives east at a speed that is 9 mph higher.
After 3 hours the distance between you and your friend is 282.78 miles.
:
let s = your driving speed
then
(s+9) = your friend's
:
In 3 hrs:
3s = your driving dist
(3(s+9) = your friend's dist
:
this is a rt triangle problem, a^2 + b^2 = c^2, where
a = 3s
b = 3(s+9)
c = 282.78
:
(3s)^2 + (3(s+9))^2 = 282.78^2
9s^2 + (3s+27)^2 = 79964.53
9s^2 + 9s^2 + 81s + 81s + 729 - 79964.53 = 0
18s^2 + 162s - 79235.53 = 0
Using the quadratic formula, I got:
s = 62 mph is your speed
:
:
Check this on your calc:
3*62 = 186 mi
3*71 = 213 mi
enter:

You have been driving at _______ mph.
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