Question

Which of the following would not be the result of a substitution in the following system?

2x + y = 7
y - x = 1

7 - 2x - x = 1
2x + x + 1 = 7
2(y + 1) + y = 7

Answer 1

2x+y=7
y-x=1

from 2nd equation
x=y-1...(3)

put this third equation in equation (1)

Answer 2

y=1+x...(4)

put this 4th equation in 2nd equation

Answer 3

finally check