# math

posted by jane

two cars leave the same point at noon. one car travels north and the other car travels east. suppose the northbound car is traveling 40mph, and after two hours, the two car are 100 miles apart.how fast is the other car going?

1. Jai

recall that speed is distance travelled over time.
let x = speed of the other car.
then we set-up the equation.
when you draw the directions they're travelling, you will form a right triangle. thus recall that in a right triangle, the hypotenuse (in this the the distance between them which is 100 miles) is given by the Pythagorean theorem:
c^2 = a^2 + b^2
we equate distances:
100^2 = (40*2)^2 + (2x)^2
10000 = 80^2 + 4x^2
10000 - 6400 = 4x^2
3600 = 4x^2
x^2 = 900
x = 30 mph

hope this helps~ :)

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