frog jump not coming out with right answers.-HELP

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olemary

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Apr 17, 2007
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I will write as in the book, then show my work, hopefully, someone can tell me what I'm doing wrong!!!
Q: at a local frog jumping contest, Rivit's jump can be approxomated by the equation y= -1/6x^2 +2x and Croak's jump can be appromimated by the equation y= -1/2x^2 +4x, where x=the length of the jump in feet and y=the height of the jump in feet.
a) which frog jumped higher? How high did it jump?
b) which frog jumped further? How far did it jump?

my work:
y=-1/6x^2 + 2x
x=-b/2(a)
=-2/2(-1/6)
x=6.02
y=-1/6(6.02)^2 + 2(6.02)
y=11.04 (FOR RIVET)

y=-1/2x^2 +4x
x=-b/2(a)
=-4/2(-.5)
x=4
y=-1/2(4)^2 + 4(4)
y= 14 (FOR CROAK)

a)Rivet jumped further with 6.02 feet
b) Croak jumped higher with 14 feet.

The correct answer according to my book....a) Croak, 8 feet (b) Rivet, 12 feet

SO WHAT DID I DO WRONG?????
 
a) You appear to be using the formula for the vertex (h, k): For y = ax<sup>2</sup> + bx + c, the value of h is given by -b / (2a). But I think you're trying so hard to avoid fractions that you're confusing yourself and making things much harder than they need to be.... :oops:

Doing the computations exactly, you should get:

. . . . .-b / (2a) = -(2) / (2(-1/6)) = 2 / (2(1/6)) = 1 / (1/6) = 6

Where did "6.02" (for Rivet) come from?

Note: If you use the exact value for h, the value for k will be easier, too. :wink:

Also, since h is the x-coordinate of the vertex, not the y-coordinate, h cannot give the height, but only the distance from the starting line at which the peak height occurred.

b) Find the x-intercepts (that is, the zeroes) of each quadratic. You'll get two solutions, only one of which is valid for the ending (that is, the landing) distance.

Eliz.
 
FROG JUMP

You asked where the 6.02 came from. The figure came from the formula x=-b/2(a)

I used -2/2(-1/6) First I must figure -1 divided by 6=.166 .166^2=-2 divided by -.332=6.02

Am I not doing that right?
 
Exactly Elizabeth's point.

1/6 is NOT 0.166

Fractions are not evil. Learn how to use them and you will confuse yourself with rounding error a lot less often.

Also, what does this whole line mean?

".166^2=-2 divided by -.332=6.02"

(1/6)^2 = 1/36. It certainly is NOT -2, nor is it -2 / -0.332.

Further -2 / (-0.332) = 6.024096386, while -2 / (-1/3) = 6

Very, very messy.
 
frog jump

This is why I asked for help! I told you all I didn't know how to do this stuff! It's been 20+ years since I was in school and I didn't even have algebra....now I've got it all big time to get my degree. I need someone who can explain things out like I'm 2!!! (which is the intellegence I feel when working these problems).

thanks,
Mary
 
Good deal. Since you are still talking to us, we must be going in a good direction. Continue to take instruction.

Here's one: Try to write what you think. One thing notation is supposed to do is organize your brain. One of my important rules is "Write only truthful equal signs." or "Never write an equal sign that is telling a lie." That's why I was picking on this "-1 divided by 6=.166 .166^2=-2 divided by -.332=6.02". It is very, very hard to tell what those "=" mean.

By the Way, Howdy Neighbor. I was just in Palmyra, last Saturday. A little down the street from you.
 
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