Question

Hiya :) Could someone help me solve this? Explain how to do it maybe? I'd appreciate it!

y = - 1/9 x^2 + 5x +3

The height y (in feet) of a ball thrown by a child is given by the equation, where x is the horizontal distance (in feet) from the starting point. What is the maximum height of the ball?


A) -165.75 ft
B) -84.75 ft
C) 50.25 ft
D) 59.25 ft

Answer 1

Since the coefficient of the x^2 is negative we know it looks kinda like this right?

Answer 2

Yes, of course. :)

Answer 3

The vertexes of course

Answer 4

So we can find this either by converting \[- 1/9 x^2 + 5x +3\] to vertex form or using a graphing calculator

Answer 5

Vertex form is a(x - h)^2 + k

Answer 6

Oh! That's..uh oh. I messed up big time. Shoot xD

Answer 7

Where ( h , k ) is the vertex. Vertexes are normally written (x,y). You want to find height so the y or k

Answer 8

Are you allowed to use a graphing calculator?

Answer 9

Yes, I'm allowed :) So we are basically solving for y then?

Answer 10

Not really, you're solving for the y coordinate of the vertex.

Answer 11

Because somehow I ended up with C as my answer

Answer 12

Here I graphed it for you https://www.desmos.com/calculator/vx4v8gwhoa

Answer 13

Just find the y coordinate of the vertex. C isnt correct

Answer 14

Okay. Thank you :)

Answer 15

So, this would be D. Not C.

Answer 16

Yup

Answer 17

Wait .. No. Nevermind .

Answer 18

Thanks.