algebra

katie123 · #1 $Old$ March 29th, 2009, 03:45 PM

How do you solve the problem below by using elimination?

11x-5y=80
9x-15y=120

please help i have no idea how to do it

stapel · #2 $Old$ March 29th, 2009, 03:59 PM

Quote:

Originally Posted by katie123 $View Post$

How do you solve the problem below by using elimination?

...i have no idea how to do it

To learn how to solve systems "by elimination", try studying some online lessons.

Long story short: Multiply one or both of the equations by values that allow for one of the variables to "cancel off" when you add down. For instance:

HTML Code:

3x + 5y = 21
2x - 4y = -4

multiply R1 by 2
multiply R2 by -3

 6x + 10y = 42
-6x +  8y = 12

add down:

 6x + 10y = 42
-6x +  8y = 12
--------------
      18y = 54

      18y = 54
      ---   --
      18    18

        y = 3

Then back-solve to find the value of x....

katie123 · #3 $Old$ March 29th, 2009, 04:08 PM

thank you