SOLUTION: After t sec, the height of a rocket launched straight upward from the ground level with an initial velocity of 76ft/sec can be modeled by the polynomial 76t-16t^2. After how many s

Question 899127: After t sec, the height of a rocket launched straight upward from the ground level with an initial velocity of 76ft/sec can be modeled by the polynomial 76t-16t^2. After how many seconds will the rocket reach a height of 18 feet above the launch (that is, equal to +18)?
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
-16t^2 + 76t = 18
-16t^2 + 76t - 18 = 0
x = 0.25, 4.5
.25sec after launch, rocket reaches 18ft

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=4624 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 0.25, 4.5. Here's your graph:

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