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Solve the following system of equations using Elimination:

[tex]\[
5x - 4y = 23
\][/tex]
[tex]\[
7x + 8y = 5
\][/tex]

A. (3, -2)
B. (3, 2)
C. (-3, -2)
D. (-3, 2)
E. No Solution
F. Infinite Solutions


Sagot :

Sure! Let's solve the system of equations using the Elimination method. The given system is:

[tex]\[ \begin{cases} 5x - 4y = 23 & \quad \text{(Equation 1)} \\ 7x + 8y = 5 & \quad \text{(Equation 2)} \end{cases} \][/tex]

Step-by-Step Solution:

1. Multiply the equations to eliminate [tex]\( y \)[/tex]:
- Multiply Equation 1 by 2 to make the coefficients of [tex]\( y \)[/tex] opposites.

[tex]\[ 10x - 8y = 46 \quad \text{(Equation 1 multiplied by 2)} \][/tex]

- Multiply Equation 2 by 1 (no change needed).

[tex]\[ 7x + 8y = 5 \quad \text{(Equation 2 unchanged)} \][/tex]

2. Add the two equations:
- Adding Equation 1 multiplied by 2 and Equation 2 will eliminate [tex]\( y \)[/tex]:

[tex]\[ (10x - 8y) + (7x + 8y) = 46 + 5 \][/tex]

This simplifies to:

[tex]\[ 17x = 51 \][/tex]

3. Solve for [tex]\( x \)[/tex]:
- Divide both sides of the equation by 17:

[tex]\[ x = \frac{51}{17} \implies x = 3 \][/tex]

4. Substitute [tex]\( x \)[/tex] back into one of the original equations:
- Use Equation 1 for substitution:

[tex]\[ 5x - 4y = 23 \][/tex]

- Substitute [tex]\( x = 3 \)[/tex] into Equation 1:

[tex]\[ 5(3) - 4y = 23 \][/tex]

This simplifies to:

[tex]\[ 15 - 4y = 23 \][/tex]

5. Solve for [tex]\( y \)[/tex]:
- Isolate [tex]\( y \)[/tex] by first moving [tex]\( 15 \)[/tex] to the right side:

[tex]\[ -4y = 23 - 15 \][/tex]

This simplifies to:

[tex]\[ -4y = 8 \][/tex]

- Divide both sides by -4:

[tex]\[ y = \frac{8}{-4} \implies y = -2 \][/tex]

So, we have found the solution:
[tex]\[ x = 3, \; y = -2 \][/tex]

6. Conclusion:
The solution to the system of equations is [tex]\( \boxed{(3, -2)} \)[/tex].

Out of the given possible solutions:
- (3, -2)
- (3, 2)
- (-3, -2)
- (-3, 2)
- No Solution
- Infinite Solutions

The correct solution is:
[tex]\[ (3, -2) \][/tex]