Question

can someone please help me?
how do i solve x^2-121=0

Answer 1

there are (at least) two ways
one way is first add121 to both sides, like this
\[ x^2 -121 +121= 0+121\]
now simplify both sides
what do you get ?

Answer 2

x^2=121.

Answer 3

but, i dont know how to simply x^2

Answer 4

by definition
\[ \sqrt{x^2} = x\]
square root "undoes" the square
but to keep things equal, we have to square both sides

Answer 5

*square root both sides

Answer 6

ohh, okay, so x=11?

Answer 7

yes, but I should mention that there are two answers to a square root
people would write
\[ x = \pm \sqrt{121}= \pm 11 \]
which is short for x=11 or x=-11
(notice -11*-11 is +121)

Answer 8

so when you square root a problem to simplify, it's both?

Answer 9

yes, when solving these type problems

btw, in theory we would do
\[ \pm\sqrt{x^2}= \pm \sqrt{121} \\
\pm x = \pm 11\]
but it turns out that we only have to +/- one side to get all of the answers
so people usually do the right side.

Answer 10

oh okay, that makes sense, thank you.