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# help

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he equation y = -16t^2 + 80t describes the height (in feet) of a projectile launched from the ground at 80 feet per second. At what $t$ will the projectile reach 36 feet in height for the first time? Express your answer as a decimal rounded to the nearest tenth.

May 21, 2019

#1
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Substitute   y = 36

36 = -16t^2+80 t      now solve for t

16t^2-80t + 36 = 0        use quadratic formula...you will find 2 values for t....one will be the popint it is rising (the first time it reaches 36 ft) and the other will be when it is coming back down

Quadratic formula   a = 16     b = - 80   c = 36

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

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May 21, 2019