To eliminate the [tex]$x$[/tex] terms and solve for [tex]$y$[/tex] in the fewest steps, by which constants should the equations be multiplied before adding the equations together?

First equation: [tex]$6x - 5y = 17$[/tex]

Second equation: [tex]$7x + 3y = 11$[/tex]

A. The first equation should be multiplied by 3 and the second equation by -5.
B. The first equation should be multiplied by 3 and the second equation by 5.
C. The first equation should be multiplied by 7 and the second equation by -6.
D. The first equation should be multiplied by 7 and the second equation by 6.



Answer :

To determine the constants by which the equations should be multiplied to eliminate the \( x \) terms, let's follow these steps:

Given equations:
1. \( 6x - 5y = 17 \) (First equation)
2. \( 7x + 3y = 11 \) (Second equation)

We want to eliminate the \( x \)-terms by making their coefficients equal and opposite. To achieve this:

1. The coefficient of \( x \) in the first equation is \( 6 \).
2. The coefficient of \( x \) in the second equation is \( 7 \).

To make these coefficients equal and opposite, we need to find numbers that can be multiplied by \( 6 \) and \( 7 \) to make their products equal in magnitude but opposite in signs:

- The least common multiple (LCM) of \( 6 \) and \( 7 \) is \( 42 \).

To get coefficients of \( 42 \) and \( -42 \):

1. Multiply the first equation by \( 7 \):
[tex]\[ 7 \cdot (6x - 5y) = 7 \cdot 17 \][/tex]
[tex]\[ 42x - 35y = 119 \][/tex]

2. Multiply the second equation by \( -6 \):
[tex]\[ -6 \cdot (7x + 3y) = -6 \cdot 11 \][/tex]
[tex]\[ -42x - 18y = -66 \][/tex]

Now, the coefficients of \( x \) in the two modified equations are \( 42 \) and \( -42 \), which will cancel each other out when the equations are added.

Hence, the correct constants to multiply the equations by are:
- Multiply the first equation by \( 7 \)
- Multiply the second equation by \( -6 \)

Thus, the correct choice is:
The first equation should be multiplied by [tex]\( 7 \)[/tex] and the second equation by [tex]\( -6 \)[/tex].

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