plugging 2 into -x^3 equals what?

👨🏻‍🏫 學術台 數學
2008-12-08 8:37 am
this is ridiculous. is it -8 or 8. I seriously don't know. do you assume its (-2)^3 or -(2)^3?
更新1:

woops. in this case they both equal 8... but you get the point, if it were -x^2 is it 4 or -4

更新2:

DANG IT i mean -8. my brain is so toasted right now. its 4 in the morning. I'm in calculus and i couldnt remember. thank you though, whoever has the top contributor badge

回答 (10)

2008-12-08 8:41 am
✔ 最佳答案
The answer is -8 in both cases.

Case 1; (-2)x(-2)x(-2) = -8
Case 2: -(2x2x2) = -8

OK?
👍 1 👎 0
2008-12-08 4:44 pm
You get -8 either way.
(-2)^3 = (-2)(-2)(-2) = -8
-(2)^3 = -(2*2*2) = -8

The correct representation is the second one. When there are no parentheses, you follow the order of operations (PEMDAS). This requires you to deal with the exponent before you deal with the minus sign.
👍 2 👎 1
2008-12-08 4:48 pm
You assume that is is -(x^3)

Since there are no brackets in the expression -x^3, you do EXPONENTS before MULTIPLICATION (represented by negative sign).

Hence it is -(x^3) and NOT (-x)^3

...or in other words, it is "the negative of x cubed" and NOT "negative x, cubed"



In your example question you would have -(2^3) which equals -8. However in this particular case if you calculated it the other way it gives the same answer, (-2)^3 = -8


>>>

EDIT:

For -x^2, the answers would differ depending on which method you use:

-x^2 is the same as -(x^2), which when x=2, the answer is -4.

(-x)^2 when x=2 gives an answer of 4.
👍 1 👎 0
2008-12-08 4:46 pm
They're both -8

(-2)^3 = (-2) x (-2) x (-2) = -8
-(2)^3 = -(2 x 2 x 2) = -8
👍 1 👎 0
2008-12-08 4:44 pm
it is -8

this can be rewritten to (-1) * (x^3) ...it is the same thing as -2 = (2) * (-1)

so you multiply -1 after you cubed x or 2 in this case.

👍 1 👎 1
2008-12-08 4:42 pm
-8


-2 x -2 x -2 = -8

differentiate it or something.
👍 1 👎 1
2008-12-08 4:40 pm
-8
👍 1 👎 1
2008-12-08 6:50 pm
-x^3
= -(2)^3
= -(2)(2)(2)
= -(4)(2)
= -(8)
= -8
👍 0 👎 0
2008-12-08 5:38 pm
As written , question has to be read as :-

- ( x ³ ) = - ( 8 ) = - 8

It is best that brackets be used in the question to avoid confusion.
👍 0 👎 0
2008-12-08 4:42 pm
I have the same confusion.
👍 0 👎 2


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