Question 773238
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Since the cars are travelling east and south, which are perpendicular to each
other, the paths of the 2 cars and the distance between them form the 3 sides of
a right triangle, with the distance "d" being the hypotenuse.
At the end of t hours, 
eastward car has travelled 40*t miles
southward car has travelled 30*t miles
Applying Pythagoras theorem
{{{d^2 = (40*t)^2 + (30*t)^2 = 2500*t^2}}}
So the expression for d is
{{{d = sqrt(2500*t^2) = 50*t}}}
Hope you got it :)
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