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What should be the first step in adding these equations to eliminate [tex]\( y \)[/tex]?

[tex]\[
\begin{array}{r}
3x + 4y = 8 \\
+6x - 2y = 9 \\
\hline
\end{array}
\][/tex]

A. Multiply the bottom equation by 2.
B. Multiply the bottom equation by 3.
C. Multiply the top equation by 6.
D. Multiply the top equation by 2.


Sagot :

To eliminate [tex]\( y \)[/tex] from the system of equations
[tex]\[ \begin{array}{r} 3x + 4y = 8 \\ 6x - 2y = 9 \\ \end{array} \][/tex]
our goal is to make the coefficients of [tex]\( y \)[/tex] in both equations equal in magnitude but opposite in sign.

The coefficients of [tex]\( y \)[/tex] are [tex]\( 4 \)[/tex] in the first equation and [tex]\(-2 \)[/tex] in the second equation. To make these coefficients equal (but opposite in sign), we can multiply the second equation by [tex]\( 2 \)[/tex]. When we do this, the coefficient of [tex]\( y \)[/tex] in the second equation will become [tex]\( -4 \)[/tex], which is opposite (in sign) to the [tex]\( 4y \)[/tex] in the first equation.

Thus, the first step is to multiply the bottom equation by [tex]\( 2 \)[/tex]:
[tex]\[ \begin{array}{r} 3x + 4y = 8 \\ 2 \cdot (6x - 2y) = 2 \cdot 9 \\ \end{array} \][/tex]
[tex]\[ \begin{array}{r} 3x + 4y = 8 \\ 12x - 4y = 18 \\ \end{array} \][/tex]

So, the correct answer is:
A. Multiply the bottom equation by 2.