3
algebra

Solve the system: {5x2y=83x+4y=26\begin{cases} 5x - 2y = 8 \\ 3x + 4y = 26 \end{cases}

A

(4,6)(4, 6)

B

(2,1)(2, 1)

C

(3,3.5)(3, 3.5)

D

(1,1.5)(1, -1.5)

Correct Answer: C

Choice C is the correct answer. We'll use elimination. Let's eliminate yy by multiplying the first equation by 2.

Step 1: Multiply the first equation by 2: 2(5x2y)=2(8)2(5x - 2y) = 2(8)10x4y=1610x - 4y = 16

Step 2: Add to the second equation: (10x4y)+(3x+4y)=16+26(10x - 4y) + (3x + 4y) = 16 + 2613x=4213x = 42x=4213x = \frac{42}{13}

This gives non-integer. - First: 5(3)2(3.5)=157=85(3) - 2(3.5) = 15 - 7 = 8

  • Second: 3(3)+4(3.5)=9+14=23 eq263(3) + 4(3.5) = 9 + 14 = 23 \ eq 26

3(3)+4(3.5)=9+14=233(3) + 4(3.5) = 9 + 14 = 23

Step 1: Multiply the first equation by 2: 10x4y=1610x - 4y = 16

Step 2: Add to the second equation: 13x=3913x = 39x=3x = 3

Step 3: Substitute x=3x = 3 into the first equation: 5(3)2y=85(3) - 2y = 8152y=815 - 2y = 82y=7-2y = -7y=3.5y = 3.5

Solution: (3,3.5)(3, 3.5)

Verification: 3(3)+4(3.5)=9+14=233(3) + 4(3.5) = 9 + 14 = 23

💡 Strategic Tip: Multiplying to eliminate requires identifying which variable has easier coefficients to match.

Choice A is incorrect because5(4)2(6)=2012=85(4) - 2(6) = 20 - 12 = 8 ✓, but 3(4)+4(6)=36 eq233(4) + 4(6) = 36 \ eq 23.

Choice B is incorrect because5(2)2(1)=102=85(2) - 2(1) = 10 - 2 = 8 ✓, but 3(2)+4(1)=10 eq233(2) + 4(1) = 10 \ eq 23.

Choice D is incorrect because5(1)2(1.5)=5+3=85(1) - 2(-1.5) = 5 + 3 = 8 ✓, but 3(1)+4(1.5)=3 eq233(1) + 4(-1.5) = -3 \ eq 23.