Question

Use the Substitution Method to solve the following system of equations.
x - 4y = 1
2x - 9y = 3

(-1, -3)

(-3, 1)

(3, 1)

(-3, -1)

Answer 1

In the first equation, we solve for x:

x = 1+4y.

As the name suggests, we plug this x-expression into the second equation:
2(1+4y) -9y
= 2 + 8y - 9y
= 2 -y
= 3 (by hypothesis).

Thus, we conclude y = -1. Then, we know x = 1+4y, thus, x = -3.
We have (-3,-1)