Use the substitution method to solve the system x = y - 4, x + 8y = 2.

A: ( 2/3, -3 1/3)

B: ( -3 1/3, 2/3)

C: Infinite solutions

D: No solutions

1 answer

To solve the system using the substitution method, we start with the two equations provided:

  1. \( x = y - 4 \)
  2. \( x + 8y = 2 \)

We can substitute the expression for \( x \) from the first equation into the second equation.

Substituting \( x = y - 4 \) into the second equation:

\[ (y - 4) + 8y = 2 \]

Now, combine like terms:

\[ y - 4 + 8y = 2 \] \[ 9y - 4 = 2 \]

Next, we solve for \( y \):

Add 4 to both sides:

\[ 9y = 6 \]

Now divide by 9:

\[ y = \frac{6}{9} = \frac{2}{3} \]

Now that we have \( y \), we can substitute it back into the first equation to find \( x \):

\[ x = y - 4 \] \[ x = \frac{2}{3} - 4 \] \[ x = \frac{2}{3} - \frac{12}{3} \] \[ x = \frac{2 - 12}{3} = \frac{-10}{3} \]

So we have:

\[ (x, y) = \left( \frac{-10}{3}, \frac{2}{3} \right) \]

Now, let's find out what these values correspond to in the answer options given:

  • A: \( \left( \frac{2}{3}, -3 \frac{1}{3} \right) \) which is \( \left( \frac{2}{3}, -\frac{10}{3} \right) \) → Not a match.
  • B: \( \left( -3 \frac{1}{3}, \frac{2}{3} \right) \) is \( \left( -\frac{10}{3}, \frac{2}{3} \right) \) → This is a match!
  • C: Infinite solutions
  • D: No solutions

Therefore, the correct answer is:

B: \( \left( -3 \frac{1}{3}, \frac{2}{3} \right) \).