Hi
When you have a system of equation, you generally have two unknowned value.
The trick is to express one letter as equal of something in the second letter.
We have two lines :
(1) : y = -5x-1
(2) : 4x-7y = 7
Here he job is half done as we have already "y" express in " x" with line (1) so : y = -5x-1
So I can rewrite line (2) as this : 4x-7y = 7
as y = -5x-1 so :
4x-7y = 7 become :
4x - 7 ( -5x-1) = 7
4x-7 * (-5x) - 7* (-1) = 7
4x +35x +7 = 7
4x +35x +7 -7 = 7-7
39x = 0
39x/39 = 0 /39
x = 0
So if X = 0 then we have in line (1) we have by replacing "x" by it's value : y = -5x-1
y = -5*0 -1
y = -1
Dont hesitate to ask in comments if it's still not clear.
