2x - y = 10

y = - x - 1

Solve the system of equations

(9, 8)

(3, - 4)

no solution

You can plug - x - 1 for y in the first equation

2x - (-x - 1) = 10

2x + x + 1 = 10

Combine

3x = 9

Divide

x = 3

Plug 3 for x in any equation (I'll use th second equation)

y = - (3) - 1

y = - 3 - 1 = - 4

x = 3; y = - 4

(3, - 4)

2x - y = 10 ... (a)

y = - x - 1 ... (b)

Substitute y = - x - 1 into equation (a)

2x - y = 10

2x - (-x - 1) = 10

2x + x + 1 = 10

3x + 1 = 10

3x = 10 - 1

3x = 9

x = 9/3 = 3. x = 3

Recall, y = - x - 1 = - 3 - 1 = - 4

Hence solution (x, y) = (3, - 4)