Question

x*(-x) = 0 right?

Answer 1

@dan815 @Euler271

Answer 2

x*x*-1 can be written as -x^2
it is only 0 if x is 0

Answer 3

well im asking because this is my question: (x-3)(x+3) +3y - x + 2 = (x-2)\[(x-3)(x+3) +3y - x + 2 = (x-2)^{2}+y\]

Answer 4

ignore that first thing :)

Answer 5

and im eliminating the brackets now...

Answer 6

so far i got 2x+3x+3xy and now im stuck

Answer 7

what are you solving for ? the variable y ?

Answer 8

x and y

Answer 9

so could you help me get rid of the brackets please? @phi

Answer 10

you are confusing me. you can solve for 2 variables only if you have 2 equations
do you have 2 equations ?

Answer 11

all i want to do for now, is get rid of the brackets :)

Answer 12

\[(x-3)(x+3) +3y - x + 2 = (x-2)^{2}+y\]

Answer 13

for that

Answer 14

you can multiply them people use FOIL

Answer 15

(x-3)(x+3) = x^2 - 9

Answer 16

im doing it a different way..
x*x
x*3
x*3y
x*-x
x*2

Answer 17

well that is a little long...

Answer 18

how can i use FOIL for this?

Answer 19

(x+3)(x-3)
First: x*x or x^2
Outer x*-3 or -3x
Inner: 3x
Last: 3*-3 = -9
add up to get
x^2 -3x+3x -9
-3x +3x is 0, so you can simplify to

x^2 - 9

Answer 20

though people memorize that (a+b)(a-b)= a^2 - b^2
that formula works for (x+3)(x-3)
they also use that formula to factor a^2 - b^2 to get (a+b)(a-b)...

Answer 21

hm okay so now i got x^2-9+3y-x+2=(x-2)^2+y

how do i get rid of the second bracket now?

Answer 22

same way... (x-2)^2 is the same as (x-2)(x-2)
use FOIL: x^2 -2x -2x +4 or x^2 -4x +4

Answer 23

oh okayyyy :)

Answer 24

x^2-9+3y-x+2=x^2-4x +4+y

Answer 25

so this is how it should look like?

Answer 26

yes
but you can simplify it. It will turn into an equation for a line

Answer 27

simplified it should look like this?

-9+2y+2=-3x+4

Answer 28

you can combine all the numbers

Answer 29

i dont understand... i am wrong?

Answer 30

you are correct. but -9 +2 is -7
if you add 7 to both sides you get
-9+2y+2=-3x+4
2y - 7 = -3x +4
2y = -3x + 11

if you now divide by 2 you get
y = (-3/2) x + 11/2
which is the equation of a line with slope -3/2 and y-intercept of 11/2

Answer 31

but you added =7 to the first equation 2 times and to the second once... you can do that?

Answer 32

+7

Answer 33

sorry

Answer 34

I was not clear. I meant we start with what you found

-9+2y+2=-3x+4

I then simplified -9 + 2 to get -7 on the left side
2y - 7 = -3x + 4

now add 7 to both sides to get
2y = -3x +11

and finally, divide both sides by 2
y = (-3/2) x + 11/2

Answer 35

ahh now i see :)

Answer 36

so 2/2 = 1 = y

Answer 37

yes, on the left side of the equation

Answer 38

but I would say 2y/2 = (2/2) * y = 1* y = y

Answer 39

i dont see how you got (-3/2) though

Answer 40

ohhh im sorry, i do

Answer 41

\[\frac{ 2y}{2} = \frac{-3x +11}{2} \]

Answer 42

nevermind, silly mistake

Answer 43

-3/2 = 0.6

Answer 44

11/2 = 5.5

Answer 45

-3/2 = -0.6

Answer 46

-3/2 is -1.5

but people often leave the answer as a fraction

Answer 47

oh, okay

Answer 48

y= 1.5x+5.5

Answer 49

y=3x

Answer 50

is that right?

Answer 51

y= -1.5x + 5.5 (you lost a minus sign)

that is as simple as you can get it, unless you have another equation

it is the equation of a line, and all the points on the line will make your original messy equation true.

Answer 52

oh but wait, i have to have a number for y and x... it dosent make sense ;/

Answer 53

@phi

Answer 54

Yes, I think you should post the original question. See if you can take a screen shot of the actual question and post it

Answer 55

\[(x-3)(x+3) +3y - x + 2 = (x-2)^{2}+y\]

Answer 56

this was the original question :) how my teacher wrote it on the board

Answer 57

and was there any other information?

Your complicated equation simplifies to what we found
y = -1.5 x + 5.5

but to find a particular x,y we need more information

here is wolfram's solution of your equation
http://www.wolframalpha.com/input/?i=%28x-3%29%28x%2B3%29+%2B3y+-+x+%2B+2+%3D+%28x-2%29%5E2%2By

Answer 58

omg im sorry, i forgot to post it!

Answer 59

\[(x-3)(x+3) +3y - x + 2 = (x-2)^{2}+y-2x+y=2\]

Answer 60

all that time D;

Answer 61

so that simplified is:
-9+3y+2=-3x+4-2x=2

Answer 62

right?

Answer 63

I would pick just one expression or the other (we only need 1 more equation)

For example, pick
(x-3)(x+3) +3y - x + 2 = 2
or
x^2 - 9 + 3y - x + 2 = 2
we can simplify

Answer 64

-9+3y+2=-3x+4-2x=2

Answer 65

it cant be this?

Answer 66

then it would be -7+3y=x=2

Answer 67

we already used the first two
\[ (x-3)(x+3) +3y - x + 2 = (x-2)^{2}+y-2x+y \]
now we want to use another equation, such as
\[ (x-3)(x+3) +3y - x + 2 = 2\]

Answer 68

We should start with the original expression... I don't see how to get to -9+3y+2=-3x+4-2x=2... that is probably not correct.

so start with
\[ (x-3)(x+3) +3y - x + 2 = 2 \]

Answer 69

how does that = 2?

Answer 70

your teacher wrote A=B=2
where A is one complicated thing, and B is another complicated thing.
but if A=B and B=2 then A=2

Answer 71

ohhh i see, okayv :)

Answer 72

we could use the other expression... I think both are equally difficult (or easy) to solve

Answer 73

so what now?

Answer 74

can you simplify
\[ (x-3)(x+3) +3y - x + 2 = 2 \]
solve for 3y

Answer 75

(x-3)(x+3)

Answer 76

you should get
(x-3)(x+3) + 3y - x +2 = 2
x^2 -9 +3y -x =0
3y= -x^2 + x + 9

Answer 77

we know from the first two equations that
y= -1.5x+5.5
use that in
3y= -x^2 + x + 9

3( -1.5x +5.5) = - x^2 + x +9 <-- replaced y with -1.5x+5.5
-4.5x + 16.5 = -x^2 + x + 9 <-- distribute the 3
x^2 -5.5x +7.5=0 <--- simplified
multiply both sides by 2 to get
2x^2 -11x +15 = 0

factor into (2x - 5)(x-3) = 0
solve for x. You get two different answers
find y using y= -1.5x+5.5