For Number one: -xy + 2x = 20, x = 5
To solve this, all we need to do is plugin 5 for every place we have x. So...
- (5)y + 2(5) = 20
-5y + 10 = 20
-5y = 10
y = -2
For number two: 4x - 3y - 10 = 1, x = -1
To solve this, we need to plugin -1 for all of the x variables. So...
4 (-1) - 3y - 10 = 1
-4 - 3y - 10 = 1
-14 - 3y = 1
-3y = 15
y = -5
For number three: 5x + 7y = -1, x = 4
We need to plugin -4 for all of the x variables. So...
5 (4) + 7y = -1
20 + 7y = -1
7y = -21
y = -3
For number four: x = 6 + xy, x = -3
Same as the other ones, just plugin -3 for all of the x variables. So...
-3 = 6 + (-3)y
-3 = 6 - 3y
-9 = -3y
3 = y
I hope this helps :)
