I only know the substitutional method so I am going to give you the answers.
1. (remember I am only using the substitutional method, I am doing the method wrong...)
x + y = 10, 3x - y = 2, 5(3x-y) = 5(2), 15x - 5y = 10, 15x -5y = x + y, 14x = 6y, x = 3/7 y , 3/7 y + y = 10, 10/7y = 10, 10 y = 70, y = 7, 14x = 42. x =3
y = 7, x = 3
2. What I know:
x + y = 6
x + 2x = 6
3x = 6
x = 2, y =4
3. I am using a video to help me remember.
x = 2y + 3 2x + 3y = -3.
-3 = 2y - x -3 = 3y + 2x
0 = - y + 3x, y = 3x
x = 2(3x) + 3, x = 6x + 3
-5x = 3, x = -3/5
y = 3(-3/5)
y = -9/5, x = -3/5
