SOLUTION: a ball tossed upward from the ground its height in feet above the ground after second is given by the quadratic function y =-3x²+42x.

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Question 1187078: a ball tossed upward from the ground its height in feet above the ground after second is given by the quadratic function y =-3x²+42x.
Found 2 solutions by Theo, ikleyn:
Answer by Theo(13342) (Show Source):
You can put this solution on YOUR website!
the equation is y =-3x²+42x.

here's what it looks like on a graph.

to solve manually, do the following.

put the equation in standard quadratic form.

that is ax^2 + bx + c = 0

a is the coefficient of the x^2 term = -3.
b is the coefficient of the x term = 42.
c is the constant term = 0 (if it's not there, it's equal to 0).

the maximum / minimum value on the graph is at x = -b/(2a).
that makes x equal to -42 / -6 = 7.

that's the value of the x-coordinate.

the value of the y-coordinate is the value you get when you replace x in the equation with 7.

y = -3x^2 + 42x becomes y = -3*7^2 + 42*7 = -147 + 294 = 147.

that's the same value you see on the graph.

your solution is that the maximum height is 147 feet.

the number of seconds it takes to get there is the value of x from x = 0 to x = 7 which is 7 seconds.

here's a reference on quadratic equations you might find helpful.

https://www.mathsisfun.com/algebra/quadratic-equation.html

Answer by ikleyn(52921) (Show Source):
You can put this solution on YOUR website!
.

Deleted, as promised.

The equation, which is given in the problem, DOES NOT describe the height of the ball as a function of time
at the Earth condition.

I do not know WHY @Theo decided to disprove my statement.

Probably, because he does not know basic Physics behind this equation.

See this link

https://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Rate-of-work-word-problems.faq.question.1187044.html

https://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Rate-of-work-word-problems.faq.question.1187044.html