(x-9)²=16 x-9=±4 What does ± mean?

x - 9 = 4

OR

x - 9 = -4

± ----- "plus or minus"

Edit
& plusmn ; ----- remove the spaces and you get ±

(x - 9)² = 16
x - 9 = ± 4 + 9

Where x - 9 = 4:
x = 4 + 9, x = 13

Where x - 9 = - 4:
x = - 4 + 9, x = 5

Answer: ± is +/-; is + or -; is positive or negative. Here x is either 13 or 5.

Proof (x = 13):
(13 - 9)² = 16
4² = 16
16 = 16

Proof (x = 5):
(5 - 9)² = 16
(- 4)² = 16
16 = 16

it means "plus or minus"
in this case it means +4 or -4
this equation will have two answers according to which value of 4 you use
you must solve for both values if this is an exam
under some circumstances one of the answers you get will not be suitable so you will be left with one answer only

PS :when you choose your best answer will you please tell everyone how you typed the plus/minus sign?

short way to write x - 9 = 4 and x - 9 = -4

± means +/- (positive or negative)
(we call it a "plus-minus sign")

It means plus or minus
Thus acceptable answers are 4 and - 4

It's also used in the Quadratic Formula, if you've done that and at the end you have to split the answer into 2. So x=

Either

etc. etc. +4 or etc. ect. -4

and, using the Quadratic Formula, you work out dimensions using the positive answer.

That's all I know.

It means that the answer can be BOTH positive and negative 4.