## anonymous one year ago A toy rocket was launched from the ground. The 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?

1. anonymous

so the 'x' coordinate of our vertex is 4... so I'm going to say the rocket would take 4 seconds to get up to maximum height...and then it will fall back down taking 4 seconds How do i know it will only take 4 seconds to get down? Well I would find out the x-intercepts of the parabola by factoring -16x^2 + 128x = 0 factor our like terms -16x(x - 8) = 0 so we have 2 equations -16x = 0 and (x - 8) = 0 well that means our 2 x intercepts are 0 and 8 So if it take 4 seconds to go up to the max height...we only have 4 seconds to fall back down Hence the answer being B

2. anonymous

Woah, Where did you get that answer from?

3. misty1212

what on earth?

4. misty1212

first coordinate of the vertex is always (i repeat always ) $-\frac{b}{2a}$

5. misty1212

do $-\frac{128}{2\times (-16)}$ and that is all

6. anonymous

@misty1212 What he did was, He went on google, Searched up my question. And some other guy that has already posted this question answered it.

7. misty1212

i love google, but $$-\frac{b}{2a}$$ cannot be that hard to compute in any case what does "the answer is B" mean in this context?

8. anonymous

9. anonymous

Thanks @LesTwins I do the same. I already got that answer but I want to double check. Quite slick.

10. anonymous

I did the math then searched with google to give u the insurance you need to get the question correct