# positive exponents

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• Oct 1st 2011, 01:32 PM
Candy101
positive exponents
Write with only positive exponents.

(3x^2 y) (-2x^-2 y)

I got -6x^2 y^2

But the teacher got -6y^2

I don't understand how he got that
• Oct 1st 2011, 01:35 PM
Plato
Re: positive exponents
Quote:

Originally Posted by Candy101
Write with only positive exponents.
(3x^2 y) (-2x^-2 y)

$(3x^2 y) (-2x^{-2} y)=(3)(-2)(x^{2-2})(y^{1+1})=-6y^2$
• Oct 1st 2011, 02:19 PM
Candy101
Re: positive exponents
Oh I see Wht I did wrong. I forgot about the x^-2 . Which cancels out!

Thanks

(2x^-2 y)^3 / -2x^-2 y^-3

For this one I can't understand why he got -4y^6/x^4

I got -4x^-4 y^-6

I know I have to flip it

So y can't I get
y^6 / 4x^4
• Oct 1st 2011, 02:24 PM
Quacky
Re: positive exponents
Quote:

Originally Posted by Candy101
Oh I see Wht I did wrong. I forgot about the x^-2 . Which cancels out!

Thanks

(2x^-2 y)^3 / -2x^-2 y^-3

For this one I can't understand why he got -4y^6/x^4

I got -4x^-4 y^-6

I know I have to flip it

So can't I got
y^6 / 4x^4

Why not learn latex, so that we can easily comprehend what you're trying to say? Is this the initial expression:

$\frac{(2x^{-2}y)^3}{-2x^{-2}y^{-3}}$
• Oct 1st 2011, 02:37 PM
Plato
Re: positive exponents
Quote:

Originally Posted by Candy101
(2x^-2 y)^3 / -2x^-2 y^-3
For this one I can't understand why he got -4y^6/x^4

Why not learn to use some basic LaTeX code.
[TEX]\frac{(x^{-2}y)^3}{(-2x^{-2}y^{-3})}[/TEX] gives $\frac{(x^{-2}y)^3}{(-2x^{-2}y^{-3})}$

$\frac{(x^{-2}y)^3}{(-2x^{-2}y^{-3})}=-\frac{y^6}{2x^4}$
• Oct 1st 2011, 02:38 PM
Candy101
Re: positive exponents
Yeah
• Oct 2nd 2011, 06:32 AM
HallsofIvy
Re: positive exponents
Quote:

Originally Posted by Candy101
Oh I see Wht I did wrong. I forgot about the x^-2 . Which cancels out!

Thanks

(2x^-2 y)^3 / -2x^-2 y^-3

For this one I can't understand why he got -4y^6/x^4

I got -4x^-4 y^-6

I know I have to flip it

So y can't I get
y^6 / 4x^4

(2x^-2 y)^3= 8x^-6y^3. The denominator, 1/(-2x^-2y^-3), becomes (-1/2)x^2y^3

8(-1/2)= -4. x^-6(x^2)= x^{-4}. y^3(y^3)= y^6

So that is -4x^{-4}y^6 which, using only positive exponents, is -4y^6/x^4. Again, 8/-2 is -4, not -1/4.