Question

If you were to use the substitution method to solve the following system, choose the new equation after the expression equivalent to y from the second equation is substituted into the first equation. 2x − 7y = 4 3x + y = −17

Answer 1

The simultaneous equations are
2x - 7y = 4         (1)
3x + y = -17       (2)

Write (2) as
y = - 3x - 17       (3)

Substitute (3) into (1).
2x - 7(-3x - 17) = 4
2x + 21x + 119 = 4
23x = -115
x = -5
This is the equation obtained after substituting y from the second equation into the first equation.
The solution for y is
y = -3(-5) - 17 = -2

Answer: x = -5

Note: The solution is x = -5,  y = -2.