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# Help

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The equation $y = -4.9t^2 + 23.8t$ describes the height (in meters) of a projectile launched from the ground at 23.8 meters per second. In how many seconds will the projectile first reach 28 meters in height?

Dec 8, 2020

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28 = -4.9t^2 + 23.8t

-4.9t^2 + 23.8t -28 = 0      quadratic formula to solve   a = -4.9    b = 23.8   c = -28

$$t = {-b \pm \sqrt{b^2-4ac} \over 2a}$$

you'll get TWO t values ....one is for the  time when proj is going up....the larger one is for when proj is coming down

Dec 8, 2020