+0  
 
+2
131
16
avatar+2046 

I tried solving these but I gave up lol I could only get to the parts where you add the x values and add the y values

For example, for number 1, 7x+-14x=-7x and 2y-3y=-1y (you would only add if there is a + right?)

And then add -10+29= 19 so I got to -7x+-1y=19 but i don't even know if I did that right. I got stuck there.

RainbowPanda  Aug 28, 2018
 #1
avatar+90969 
+4

The keys to  solving  these

(1)  line up all variables  on  one side of the equation and constants on the other

(2)  pick a variable to eliminate....either will do....this is the REAL key

(3) not a necessity...but I always like to get rid of fractions, too, before  I start

 

7x + 2y  = -10

-14x  - 3y  = 29

 

I see that if I multiply the top equation by  2 and add it to the second equation,  the "x" term will disappear..so

 

14x  + 4 y  = -20

-14x - 3y  = 29    add these  and we get

 

y  = 9

 

To find x...we can  use any equation...so...

 

7x + 2(9)  = -10

7x + 18  = -10

7x = -28

x  = -4

 

So.....(x, y)  =(-4, 9)

 

Do you want to try a couple on your  own, RainbowPanda  ??

 

 

cool cool cool

CPhill  Aug 28, 2018
edited by CPhill  Aug 28, 2018
 #2
avatar+3270 
+2

@CPhill, 29 or -29? This was in step 2.

(2) Multiply the second equation by 2, so: -9x-14y=-29, 10x+7y=-2, -9x-14y=-29, 20x+14y=-4..

So, adding: y gets canceled, and 11x=-33, \(x=-3\), so y= -9(-3)-14y=-29, 27-14y=-29, 14y=27+29, 14y=56, \(y=4.\)

tertre  Aug 28, 2018
edited by tertre  Aug 28, 2018
edited by tertre  Aug 28, 2018
edited by tertre  Aug 28, 2018
 #3
avatar+90969 
+2

Sorry.... typo...should be 29....

 

cool cool cool

CPhill  Aug 28, 2018
 #4
avatar
-2

Nobody is going to help you. You should probably pay more attention in class. I guess that means you're kind of dumb. πŸ’ΈπŸ’°πŸ’ŽπŸ˜ŽπŸ˜ˆπŸ’©.

 

Can you answer me this, what is 2+6578901+51784946% and -17264967+-837956881868078.

Guest Aug 28, 2018
 #7
avatar+90969 
+3

Well, Guest.....maybe everyone isn't as brilliant as you are...besides....this elimnation stuff isn't that easy when you're new to  it....

 

 

cool cool cool

CPhill  Aug 28, 2018
 #5
avatar+90969 
+2

4)  -20  + 10 x  = -10y   

      45  = 6x  - 27 y

 

Rearrange each as

 

10x  + 10y   = 20

6x  - 27 y  = 45

 

I see that I can divide the top equation  by 10  and the bottom by 3  to  get :

x + y  = 2

2x - 9y  = 15

 

I see that I can  eliminate  'x"  by multiplying the top equation by  -2

-2x - 2y  = -4

2x - 9y  = 15     add these

 

-11y = 11     

y = -1

 

And using any equation to find x, we  have

 

x + y  = 2

x + (-1)  = 2

x - 1  = 2

x  =3

 

So  (x,y)  =  (3 , -1)

 

Do these steps help  ???

 

 

cool cool cool

CPhill  Aug 28, 2018
 #6
avatar+3270 
+3

(4) Hint: Try to rearrange the equation, the first and second: Take -10y to the other side, and see what you can do.

tertre  Aug 28, 2018
 #8
avatar+90969 
+2

Thanks, Tertre  !!!!

 

 

cool cool cool

CPhill  Aug 28, 2018
 #9
avatar+3270 
+2

Welcome, CPhill!

tertre  Aug 28, 2018
 #10
avatar+2046 
+2

Thank you so much for your help, both of you. I have tried it and yet i'm still too dumb to solve these. >.<

RainbowPanda  Aug 28, 2018
 #11
avatar+90969 
+3

You're not  "dumb"....it's just hard to  get the hang of this...

 

I'll do   2)  and  3).....maybe that will help some

 

2)  - 9x  - 14y   = -29

     10x + 7y  =   -2

 

Ok....do you see that we  can  eliminate y  by  multiplying the second equation by -2  ??...so we have

 

-9x - 14 y  =  -29

20x  + 14y  = -4     add these

 

11x  = -33   divide by 11

x  = -3

 

Using  10x + 7y   = -2 to find y, we have

10(-3) + 7y  = -2

-30  + 7y = -2    add 30  to both sides

7y  = 28   divide by 7

y  = 4

 

So...(x, y)  = ( -3, 4)

 

 

cool cool cool

CPhill  Aug 28, 2018
 #12
avatar+90969 
+3

3)   0 =  -36x + 14y  + 8

      0 =  18y  - 9  - 27x

 

Rearrange these as

 

36x - 14y  = 8

27x  - 18 y   = -9

 

Divide the first equation through by 2  and the second one through  by 9

 

18x  -  7y   =  4

3x   -  2y   =  -1

 

I see that we  can  get  "-18x"  by multiplying the second equation by  -6  ...so we have

 

18x - 7y   =  4

-18x + 12y  = 6    add these

 

 

5y  = 10    divide by 5

y  = 2

 

Using   3x  - 2y  =  -1   to find x, we have

 

3x  - 2(2)  = -1

3x  - 4  =  -1

3x  = 3   divide by 3

x  = 1

 

So  (x,y)  = ( 1, 2)

 

 

cool cool cool

CPhill  Aug 28, 2018
 #14
avatar+2046 
+3

It's just that some of the problems are different so it makes it harder to understand and to know you are doing the problems correctly because you can't go off of one problem if they are even the slightest bit different. Am I even making sense right now xD

Thank you for helping~

RainbowPanda  Aug 28, 2018
 #15
avatar+90969 
+1

Yep...that is what makes this a little difficult...there  isn't a "cookbook"  method of doing these....

 

Don't worry...you will get the hang of it....!!!!!

 

Just practice a few...

 

 

cool cool cool

CPhill  Aug 28, 2018
edited by CPhill  Aug 28, 2018
 #16
avatar+2046 
+1

Problem is there is also other ways of solving these problems like solving the system of equations by substitution and of course elimination. 

RainbowPanda  Aug 28, 2018
 #13
avatar+621 
+3

For (3). Just take the constant to the other side, you're left with x and y= constant.

Here, I'll show you!  

 

0=-36x + 14y + 8 

0 = 18y -9 -27x

 

Best thing to do first: 36x - 14y = 8 - 0, 36x - 14y = 8

And, for the second equation: 27x - 18y = 0+9, 27x - 18y = -9.

 

Now, divide the first equation by 2 and the second equation by 9, because the x will end up as a canceling factor.

 

So, 18x-7y=4, 3x-2y=-1, try to make both x's equal, subtract find x, then solve for y!

mathtoo  Aug 28, 2018

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