Quadratic Functions

[melanies88]

Hello,

I'm stumped by the following problem. Can someone please help walk me through it? I know the answers, but I can't figure out how to get there.

A ball is thrown upward and outward from a height of 6 feet. The height of the ball, f(x), in feet, can be modeled by:
f(x)=-0.8x^2+3.2x+6

Where x is the ball's horizontal distance, in feet, from where it was thrown.

A) What is the maximum height of the ball and how far from where it was thrown does this occur? (Answer: 9.2ft; 2 ft)

B)How far does the ball travel horizontally before hitting the ground? (Answer: 5.4 ft)

Thank you!

 

[HallsofIvy]

melanies88, why have you not shown any work of your own? If you honestly have no idea how to solve a quadratic equation (the second part of this problem) I don't see how you can be expected to answer the first part, which requires "completing the square". Do you know what "complete the square" means?

 

[Quaid]

f(x) = -0.8x^2 + 3.2x + 6

A) What is the maximum height of the ball and how far from where it was thrown does this occur? (Answer: 9.2ft; 2 ft)

Hi Melanie:

You can answer this first part by using the formula for the x-coordinate of the vertex:

x-coordinate of the vertex = -B/(2A)

Substitute the known values for A and B into this formula, and simplify.

Then calculate the value of function f at the vertex by substitution.

B) How far does the ball travel horizontally before hitting the ground? (Answer: 5.4 ft)

As others have mentioned, you can use the Quadratic Formula for part B.

Please show us how far you can get.

Also, check out the forum guidelines; here's a link to the summary page.

Cheers

 

[Quaid]

Hi Melanie,

Were you able to finish? Do you need more help, with these questions?

Cheers