Solve the system of equations.

6x – 3y = 3

–2x + 6y = 14

What number would you multiply the second equation by in order to eliminate the x-terms when adding to the first equation?

What number would you multiply the first equation by in order to eliminate the y-terms when adding to the second equation?

1 answer

To eliminate the \( x \)-terms when adding the two equations, we can look at the coefficients of the \( x \) terms in both equations. The first equation is:

\[ 6x - 3y = 3 \quad \text{(Equation 1)} \]

The second equation is:

\[ -2x + 6y = 14 \quad \text{(Equation 2)} \]

Eliminate \( x \)-terms

  1. The coefficient of \( x \) in Equation 1 is \( 6 \).
  2. The coefficient of \( x \) in Equation 2 is \( -2 \).

To eliminate \( x \)-terms, we need these coefficients to be the same (but opposite in sign). We can multiply Equation 2 by \( 3 \) because:

\[ 3(-2x) = -6x \]

Now, if we multiply Equation 2 by \( 3 \), we get:

\[ 3(-2x + 6y) = 3(14) \]

This results in:

\[ -6x + 18y = 42 \quad \text{(Modified Equation 2)} \]

Now we can add the modified Equation 2 to Equation 1:

\[ (6x - 3y) + (-6x + 18y) = 3 + 42 \]

The \( x \) terms will cancel out, allowing us to solve for \( y \).

Thus, you would multiply the second equation by \( 3 \).


Eliminate \( y \)-terms

To eliminate the \( y \)-terms when adding the two equations, we look at their coefficients. The first equation has a \( -3y \) and the second equation has a \( 6y \).

  1. To eliminate \( y \)-terms, we can find a common multiple of the coefficients \( -3 \) and \( 6 \). The least common multiple is \( 6 \).
  2. To do this, we can multiply the first equation by \( 2 \) because:

\[ 2(-3y) = -6y \]

Now, if we multiply Equation 1 by \( 2 \), we get:

\[ 2(6x - 3y) = 2(3) \]

This results in:

\[ 12x - 6y = 6 \quad \text{(Modified Equation 1)} \]

Now we can add the modified Equation 1 to Equation 2 to eliminate \( y \):

\[ (12x - 6y) + (-2x + 6y) = 6 + 14 \]

The \( y \) terms will cancel out, allowing us to solve for \( x \).

Thus, you would multiply the first equation by \( 2 \).

Summary

  • Multiply the second equation by \( 3 \) to eliminate \( x \)-terms.
  • Multiply the first equation by \( 2 \) to eliminate \( y \)-terms.