SOLUTION: The height of an object thrown in the air is given by h = t2 � 7t + 3, where h is in feet and t is the time in seconds the object has been in motion. At what time (to the nearest

Question 224467: The height of an object thrown in the air is given by h = t2 � 7t + 3, where h is in feet and t is the time in seconds the object has been in motion. At what time (to the nearest tenth) is the object 10 feet in the air?
Answer by drj(1380) (Show Source): You can put this solution on YOUR website!
The height of an object thrown in the air is given by , where h is in feet and t is the time in seconds the object has been in motion. At what time (to the nearest tenth) is the object 10 feet in the air?

Step 1. Substitute into .

Step 2. Then, which is quadratic equation with two solutions.

The final quadratic equation is after subtracting 10 from both sides of the equation.

Step 3. To solve, use the quadratic formula given as

where a=1, b=-7, and c=-7

Solved by pluggable solver: SOLVE quadratic equation with variable

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=77 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 7.88748219369606, -0.887482193696061. Here's your graph:

Selecting the positive time is 7.9 seconds

Step 4. ANSWER: The time is 7.9 seconds.

I hope the above steps were helpful.

For FREE Step-By-Step videos in Introduction to Algebra, please visit http://www.FreedomUniversity.TV/courses/IntroAlgebra and for Trigonometry visit http://www.FreedomUniversity.TV/courses/Trigonometry.

Good luck in your studies!

Respectfully,
Dr J
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