x + y = 7
x- 3y = -1
We can solve this by elimination or substitution.
ELIMINATION
We will have to subtract the first equation from the second or vice versa.
x + y = 7
- (x- 3y = -1)
x + y = 7
-x + 3y = 1
Adding all the like terms
0 + 4y = 8
4y = 8
y = 8/4
y = 2
x + y = 7
x + 2 = 7
x = 7 - 2
x= 5
SUBSTITUTION
from the 1st equation , we can write x = 7- y
Substituting this value of x into the 2nd equation, we will have,
x- 3y = -1
(7 - y) - 3y = -1
7 - y - 3y = -1
7 - 4y = - 1
- 4y = -1 - 7
-4y = - 8
y = -8 / - 4
y = 2
x + y = 7
x + 2 = 7
x = 7 - 2
x + y = 7
x + 2 = 7
x = 7 - 2
x= 5
ANSWER
Using the two methods , we arrive at the same answer.
x= 5
y = 2