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Math help ( easy and quick)

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Canuker
Posts: 4730 - Karma: 165
I need to know this quick

4(-4.2)^3 + 4(-4.2)^2 =???????

i know the answer is  -225.79200 , but i keep getting 366.912 and its pissing me the fuck off because i have gone over it a million times and this is the only question out of all of them i have got wrong but i have no idea what i did wrong. so can some ne give me a quick little walk through, a mod can delete after i get an answer.

thanks!
Feb 14 2008 10:09PM
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THATS_STREET
Posts: 2250 - Karma: 33
69
Feb 14 2008 10:10PM
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shibby
Posts: 7088 - Karma: -19
Priority of operations, PEDMAS.
Feb 14 2008 10:12PM
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Avifarer
Posts: 5926 - Karma: 598
isnt it bedmas?
Feb 14 2008 10:13PM
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proZach
Posts: 7163 - Karma: 917

4(-4.2)^3 + 4(-4.2)^2 =???????

the second part = 70.56, the first is -296.352.

you multiply -4.2 by -4.2 by -4.2 then by 4 (order of operations).

then you add it to

-4.2 by -4.2 by 4.

the first part is - because negative x negative x negative is a negative.

that makes no sense but its right. its just hard to type out.

Feb 14 2008 10:14PM
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anxju
Posts: 9371 - Karma: 61
pemdas!!!

please excuse my dear aunt sally.

or

parenthesis exponents multiplication division addition subtraction
Feb 14 2008 10:15PM
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Canuker
Posts: 4730 - Karma: 165

BEDMAS

brackets, exponents, multiplication, division, addition, sebtraction

either way works

and this is what i got

X= -4.2      and for those of you who dont know ^= to the power of

Question: 4X^3 + 4X^2
= 4(-4.2)^3 + 4(-4.2)^2

= 4(74.088) + 4(17.64)

= 296.352 + 70.56                          

= 366.912


i dont get it because by the thrid step the first part is already greater than the answer.

Feb 14 2008 10:21PM
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Thomson.
Posts: 4634 - Karma: 227
It's to the third power so it stays negative.  The answer is -366.912.
Feb 14 2008 10:32PM
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anxju
Posts: 9371 - Karma: 61
bingo. negative times an odd number will always be negative
Feb 14 2008 10:35PM
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ajax
Posts: 2850 - Karma: 1,236
^no that's not right either.
4(-4.2)^3 + 4(-4.2)^2 =???????

first (-4.2)^3= -74.088

-74.088(4)= -296.352

-296.352+4(-4.2)^2

-296.352+4(17.64)

-296.352+70.56= -225.792
Feb 14 2008 10:40PM
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Goody
Posts: 30 - Karma: 10
When you put the negative 4 to the power of 3 into your calculator make sure the negative sign is inside the bracket then you will get the right sign. ex (-4)^3
Feb 14 2008 10:44PM
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skithedirt
Posts: 1759 - Karma: 382
this kid knows whats up thats why u keep getting 366
Feb 14 2008 11:27PM
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coolhandluke
Posts: 4465 - Karma: 153
you should check your calculations

how did you multiply a negative number by an even number and get a negative?  it would be a positive number.

(-74.088 x 4) does not equal -296.352


go get a abacus
Feb 14 2008 11:58PM
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ryano
Posts: 4465 - Karma: 1,535
4(-4.2)^3 + 4(-4.2)^2 =???????

4(-4.2)^3 = -318.028

4(-4.2)^2 = +70.65

-318.028 + 70.65 = 247.378
Feb 15 2008 12:04AM
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ryano
Posts: 4465 - Karma: 1,535
wait....



4(-4.2)^3 = -296.325

4(-4.2)^2 = +70.65

-296.325 + 70.65 = 225.702

Feb 15 2008 12:07AM
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coolhandluke
Posts: 4465 - Karma: 153
okay.  lines 2 and 3 are wrong.  try again.
Feb 15 2008 12:09AM
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ryano
Posts: 4465 - Karma: 1,535
i screwed up again.. sorry...


4(-4.2)^3 = -296.325

4(-4.2)^2 = +70.65

-296.325 + 70.65 = 225.792
Feb 15 2008 12:09AM
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ryano
Posts: 4465 - Karma: 1,535
ok....explanation...

-4.2 * -4.2 * -4.2 = -74.088...cuz an odd number of negatives stay negative. multiply that by four and you get -296.325

-4.2 * -4.2 = 17.64...an even number of negatives make a positive number. multiply that by four and you get +70.65

add the negative and the positive number and you get 225.792
Feb 15 2008 12:15AM
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coolhandluke
Posts: 4465 - Karma: 153
70.65 or 70.56?
Feb 15 2008 12:15AM
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ryano
Posts: 4465 - Karma: 1,535
i changed it...again. read the explanation.
Feb 15 2008 12:18AM
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coolhandluke
Posts: 4465 - Karma: 153
for some reason i read (-74.088*4) as (-74.088^4) wow shoot me in the balls

mea culpa
Feb 15 2008 12:19AM
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ryano
Posts: 4465 - Karma: 1,535
haha uhhh sure....do you get it now? haha.


i'm like barely passing pre calc/trig...this made me feel smart. woo
Feb 15 2008 12:24AM
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coolhandluke
Posts: 4465 - Karma: 153
yeah but check the .56 versus .65
fuck this my brain quit on me years ago, if i can't do it on my fingers then fuck it

Feb 15 2008 12:30AM
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ryano
Posts: 4465 - Karma: 1,535
yeah i know. i ly switched it..


haha yeah i know what you mean.
Feb 15 2008 12:31AM
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Celone
Posts: 1998 - Karma: 114
its actually....

Please
Excuse
My
Dear
Aunt
Sally
Feb 15 2008 1:41AM
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leckett1
Posts: 6476 - Karma: 294
It's PEDMAS in french because "brackets" is "parenthese"
Feb 15 2008 2:00AM
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