Variable Elimination A8D561
1. The problem asks which method eliminates one of the variables in the system of equations:
Equation A: $5x + 9y = 12$
Equation B: $4x - 3y = 8$
2. To eliminate a variable, we multiply the equations by constants so that the coefficients of either $x$ or $y$ become opposites and then add the equations.
3. Check each method:
(1) Multiply equation A by $-\frac{1}{3}$:
$$-\frac{1}{3} \times (5x + 9y) = -\frac{5}{3}x - 3y$$
Add to equation B:
$$(4x - 3y) + (-\frac{5}{3}x - 3y) = (4 - \frac{5}{3})x + (-3y - 3y) = \frac{12}{3}x - \frac{5}{3}x - 6y = \frac{7}{3}x - 6y$$
The $y$ terms do not cancel, so no elimination.
(2) Multiply equation B by 3:
$$3 \times (4x - 3y) = 12x - 9y$$
Add to equation A:
$$(5x + 9y) + (12x - 9y) = 17x + 0y$$
The $y$ terms cancel, so $y$ is eliminated.
(3) Multiply equation A by 2:
$$2 \times (5x + 9y) = 10x + 18y$$
Multiply equation B by -6:
$$-6 \times (4x - 3y) = -24x + 18y$$
Add:
$$(10x + 18y) + (-24x + 18y) = -14x + 36y$$
No variable eliminated.
(4) Multiply equation B by 5:
$$5 \times (4x - 3y) = 20x - 15y$$
Multiply equation A by 4:
$$4 \times (5x + 9y) = 20x + 36y$$
Add:
$$(20x - 15y) + (20x + 36y) = 40x + 21y$$
No variable eliminated.
4. Therefore, method (2) eliminates variable $y$.
Final answer: Method (2)