Question

function f(x) = -16x2 + 128x shows the height of the rocket f(x), in feet, from the ground at time x seconds. What is the axis of symmetry of the graph of f(x), and what does it represent?


x = 8; it takes 8 seconds to reach the maximum height and 8 seconds to fall back to the ground

x = 4; it takes 4 seconds to reach the maximum height and 4 seconds to fall back to the ground

x = 8; it takes 8 seconds to reach the maximum height and 16 seconds to fall back to the ground

x = 4, it takes 4 seconds to reach the maximum height and 8 seconds

Answer 1

I think A

Answer 2

what did you get?

Answer 3

any answer changes?

Answer 4

No idea what you jst did? You added x, I don't see it

Answer 5

Let me delete and redo it for you

Answer 6

y= ax^2 + bx + c
do you know this formula?

Answer 7

Yep

Answer 8

Good, next step

this is the formula for finding axis of symmetry:
axis of symmetry equation is

x= -b/ 2a

any questions?

Answer 9

Nope

Answer 10

Ok, now , look back at the equation

f(x) = -16x2 + 128x
a= -16
b= 128

plug a and b in to find it.

So far so good.

Answer 11

so plug a and b to the axis of symmetry equation

x= -b/ 2a

Answer 12

y= ax^2 + bx + c
y= (-16)x^2 + (128)x + c

Answer 13

Yes, that's right.

Answer 14

x= -b/ 2a
x= -(128)/ 2(-16)

Answer 15

yes, correct.

Answer 16

Solve it now?

Answer 17

go ahead :)

Answer 18

x= -b/ 2a
x= -(128)/ 2(-16)
x = -128/-32
x = 4

Answer 19

perfect, so your answer changes to ?

Answer 20

A, B ,C or D?

Answer 21

B Or D

Answer 22

look at this graph here
http://www.skwirk.com/content/upload/images/Secondary/NSW/Year_10/Maths/graphing/tp3/ch2/tp3ch2_image1.jpg

Notice that axis of symmetry divides the parabola into halves. Left side = right side.

Answer 23

so, it takes 4 seconds to go up, 4 seconds to go down

Answer 24

Yes I see what you mean

Answer 25

so B, yes? no? :)

Answer 26

So b yes