3
algebra

Solve by elimination: {2x+5y=212x5y=9\begin{cases} 2x + 5y = 21 \\ 2x - 5y = 9 \end{cases}

A

(2,10)(2, 10)

B

(4,18)(4, 18)

C

(3,14)(3, 14)

D

(1,12)(1, 12)

Correct Answer: C

Choice C is the correct answer. To find the intersection, we set the two expressions for yy equal to each other.

Step 1: Set the equations equal: 4x+2=x+114x + 2 = x + 11

Step 2: Solve for xx: 4xx=1124x - x = 11 - 23x=93x = 9x=3x = 3

Step 3: Find yy using either equation (using the second): y=3+11=14y = 3 + 11 = 14

Solution: (3,14)(3, 14)

Verification: 14=4(3)+2=12+2=1414 = 4(3) + 2 = 12 + 2 = 14

💡 Strategic Tip: The intersection point is where both lines have the same coordinates.

Choice A is incorrect because10=4(2)+2=1010 = 4(2) + 2 = 10 ✓, but 10 eq2+11=1310 \ eq 2 + 11 = 13.

Choice B is incorrect because18=4+11=15 eq1818 = 4 + 11 = 15 \ eq 18.

Choice D is incorrect because12=1+11=1212 = 1 + 11 = 12 ✓, but 12 eq4(1)+2=612 \ eq 4(1) + 2 = 6.