need help with word problems

Mathematics
Tutor: None Selected Time limit: 1 Day

The expression 2x2 – 10x – 28 can be used to model the height of a ball thrown in the air after x seconds. Use the quadratic formula provided below to Xigure out how long will it take for the ball to hit the ground.Use a=2, b=-10, and c=-28.Providethe positive solution only. 

Jun 18th, 2015

Thank you for the opportunity to help you with your question!

2x^2 - 10x - 28 = 0 (original equation)

(2x + 4)(x - 7) = 0 (factor)

x -7 = 0 (set the positive solution to zero)

x - 7 + 7 = 0 + 7

x = 7 seconds

This is the only positive solution,  the other solution would be -2, but since they are asking for the positive solution ONLY (which makes since we are talking about x= time in seconds it takes for a ball to hit the ground (time is always positive).

Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 18th, 2015

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