Adding linear equations? 3x+y=7, x-2y=4; 2x+3y=-1, x+5y=3

[vnesss82]

This is my first time on this site but I'm desperate Math just isn't my subject!!! I'm currently adding linear equations and I'm kinda lost don't know where to start really?
For EX:
3x + y = 7
x -2y = 4
??????????

2x + 3y = -1
x + 5y = 3
???????????

I know that you have to eliminate either x or y but multiplying by a negative or positive to cancel but I just don't know where to start? Please Help!!!

 

[Deleted member 4993]

This is my first time on this site but I'm desperate Math just isn't my subject!!! I'm currently adding linear equations and I'm kinda lost don't know where to start really? For EX:

3x + y = 7
x -2y = 4
??????????

2x + 3y = -1
x + 5y = 3
???????????

I know that you have to eliminate either x or y but multiplying by a negative or positive to cancel but I just don't know where to start? Please Help!!!

review the process at:

http://www.purplemath.com/modules/systlin5.htm

If you are still stuck, write back showing your work and indicate exactly where you are stuck.

 

[fasteddie65]

3x + y = 7
x - 2y = 4

To solve this system, you cannot simply add the equations. The idea is to eliminate one of the variables. Try to get the coefficients of x or y to be the same. For example, multiplying the first equation by 2 gives: 6x + 2y = 14. Now we can add this new equation to the second equation and get: 7x = 18. The answer for x is 18/7.

Now substitute 18/7 for x in either of our original equations to find y. 18/7 - 2y = 4. -2y = 10/7 y = -5/7

Ugly numbers, but you get the idea.