I want to know if i am rite
4. The total consumption of fossil fuels in the United States per year can be represented by the function C(x) = 0.0439x3 – 1.4911x2 + 14.224x + 41.76, where x is the number of years after 1970, and C(x) represents the amount of energy consumed in quadrillions of BTUs (or “quads”). In 1979, the U.S. consumed 81 quads of energy.
Subtract C(x) – 81 and write down the resulting function. Since you know that 9 is a root of this function, find the other two roots. In what year after 1979 did the U.S. consumption of energy also reach 81 quads?

- anonymous

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- anonymous

looks good to me. want the computation?

- anonymous

can you work this problem out?

- anonymous

well except it is not what i get

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## More answers

- anonymous

bare with me, i going write i have so far

- anonymous

let me try again and make sure i have it correct

- anonymous

C(x) = 0.0439x3 – 1.4911x2 + 14.224x + 41.76

- anonymous

so what you do is, substract 81 from 41.79

- anonymous

\[C(x)=.0439x^3-1.4991x^2+14.224x+41.76\] is that right?

- anonymous

i mean before you subtract is that correct?

- anonymous

you going have c(c) 0.0439x^3-1.4911x^2+14.224-39.28
now you use syntethic divicion,
we know 9 is a root of this function

- anonymous

yes that would be correct. if C(9) = 81

- anonymous

9] 0.0439 -1.4911 +14.224 -39.28

- anonymous

but it doesn't seem to be according to my calculation let me check again

- anonymous

no the first question

- anonymous

when you do syntethic division, you get 0

- anonymous

then you are correct!

- anonymous

and teh giving you an extreme equation, and know you can find both root,
0.0439^2-1.096x+8.36

- anonymous

you did the syntethinc division, and you got 0, correct?

- anonymous

you did the syntethinc division, and you got 0, correct?

- anonymous

you did the syntethinc division, and you got 0, correct?

- anonymous

must be typing something in wrong because i do not get zero

- anonymous

ok , type what you doing

- anonymous

close, but i get C(9)=-.04 but that is probably close enough.
you get 0 exactly?

- anonymous

so you get 0?

- anonymous

close to 0 , is not enough..

- anonymous

ooho i see

- anonymous

41.76-81=-39.24 not -39.28

- anonymous

le't try it again, 9] 0.0439 -1.4911 +14.224 +39.28

- anonymous

last number should be 39.24

- anonymous

use your calculator, i dont knohere mine is

- anonymous

then it will work

- anonymous

i did and it works

- anonymous

oh good, oh graph, yeah is -39.24, i thought it was an 8

- anonymous

whew. then you get 0 i checked already

- anonymous

get \[0.04390*x^2-1.096x+4.36\]

- anonymous

yeah, now what, guadratic formula?

- anonymous

yes what a pain. hold on and i will cheat if you like

- anonymous

lol

- anonymous

ikr, better then factoring at least...

- anonymous

looks like x=20 or x = 4.966 rounded

- anonymous

a miracle. 20 is exact!

- anonymous

so going back to the problem, those are the root, you did quadratic formula?lol

- anonymous

we must bei n the right tract

- anonymous

so it must factor as \[(x-20)(.0439x-.218)\]

- anonymous

no i didn't use the quadratic formula because i would have no patience for that

- anonymous

i used maple

- anonymous

lol, so wee know both root that were missing, the is really the aswner?

- anonymous

yup that is it

- anonymous

just changing them to word, and the will do it, thx man.

- anonymous

must be. you can check easily (more or less) that 20 is a zero of
\[.0439x^2-1.096x+4.36\] so as you know it must factor as \[(x-20)(something)\] and you have no choice for the something

- anonymous

good luck

- anonymous

oh crap, we are not,done, remember it ask you in qhat yesterday,

- anonymous

oh crap, we are not,done, remember it ask you in qhat yesterday,

- anonymous

oh crap, we are not,done, remember it ask you in qhat yesterday,

- anonymous

oh crap, we are not,done, remember it ask you in qhat yesterday,

- anonymous

oh crap, we are not,done, remember it ask you in qhat yesterday,

- anonymous

lol, lagg, year*

- anonymous

lol, lagg, year*

- anonymous

you still here?

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