SOLUTION: I have to do some problems like these two. Can anyone help me threw the steps on both of these so that I know how to do them. example 1 Solve the system. x + y = 9 x – y

Algebra ->  Coordinate Systems and Linear Equations -> SOLUTION: I have to do some problems like these two. Can anyone help me threw the steps on both of these so that I know how to do them. example 1 Solve the system. x + y = 9 x – y       Log On


   

Question 29018: I have to do some problems like these two. Can anyone help me threw the steps on both of these so that I know how to do them.
example 1
Solve the system.
x + y = 9
x – y = 3

Example 2
Solve the system by addition.
–4x + 5y = 1
x – 4y = 19







Answer by wuwei96815(245) About Me  (Show Source):
You can put this solution on YOUR website!
These types of problems are best solve using elimination and substitution.

In the elimination part we have to eliminate one of the varibles so that we can solve for the other. When we add x+y=9 and x-y=3, we get 2x =12. What happened to the y's? They were eliminated (y-y=0). Now you can easily solve for x.
2x = 12
x = 6

Since we have the value of one of the variables, we can use substituion to find the other.
x+y=9
(6)+ y = 9
y=9+6 = 15

The second problem is more difficult because simply adding the equations together will not eliminate either variable. In the second problem try multiplying the second equation by 4 and then proceeding. Let me know how you make out.