negative indices

[boobesque]

7^2 � 7^-5 = 7^-3
apparantly. To me this is incorrect. when dividing indices of the same type (7), you subtract the powers. now, 2 minus negative 5 should equal positive 3 yes? if the 5 was positive then the answer would be 7^-3. Is this correct or am i missing something

[fo3nix]

No, there should be a multiplication sign where the plus sign is.

[fo3nix]

Oops ignore that.

For the indices you have, a multiplication should be where the division is.

7^(2 minus (minus 5) = 7^(2+5) = 7^7

[tony1941]

.......or even the division sign! Yes, 7^2*7^-5=7^-3.
As printed, 7^2 / 7^-5=7^7
The clue to remembering it is to write it as a fraction:-
7^2
-----
7^-5
and then multiply above and below by the inverse of the denominator (7^5) which makes the numerator =7^7 and reduces the denominator to 7^0 which of course =1.
(well it seemed simple when I started, sorry)
Tony

[boobesque]

7^(2 minus (minus 5) = 7^(2+5) = 7^7. that makes sense. so the answer to the equation above (7^-3) is for 7^2 TIMES 7^-5. Thats what i thought but my source suggested otherwise and i thought i had better make sure. thanks

btw
The clue to remembering it is to write it as a fraction:-
7^2
-----
7^-5
and then multiply above and below by the inverse of the denominator (7^5) which makes the numerator =7^7 and reduces the denominator to 7^0 which of course =1.

i blanked out after the first few lines of that

[jake-the-peg]

For what it's worth when I saw that I thought

"..divide by 7 to the minus 5......oh - just change the -5 to + 5 and change the divide to a multiply...so 7 to the 2 times 7 to the 5 is 7 to the 7"

If that's more confusing ignore me

[Peter Pedant]

yeah boobth you've got it

7 - 2 is 5

and 7 - - 2 is 9

[clearly they cant be the same or else -1 = +1, is this a logical step too far ?)

[con-amca]

Rules of indices:

x^a times x^b = x^a+b

x^a times x^-b = x^a-b

x^a divided by x^b = x^a-b

x^a divided by x^-b = x^a+b

[boobesque]

if anyone is still reading this post, what about (y^-n)^-x?

[con-amca]

(y^-n)^-x = y^nx

e.g. y = 4, n = 3, x = 2

(4^-3)^-2 = (1/4^3)^-2 = 1/64^-2 = 64^2 = 4096

and

4^3x2 = 4^6 = 4096

I hope you can follow that - I'm having trouble!

[knobbynonuts]

e eagles m c hammer squared gedda life boobssssss anyway what you doing on this thread
Yours truely knobbynonuts
and dont flash your signs or co signs in front of me again lolllllll