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Set 17: Systems of Equations

Explanation

Answer: B

Which system has infinitely many solutions?

I. {y=6x+2y=6x5\begin{cases} y = 6x + 2 \\ y = 6x - 5 \end{cases}

II. {y=6x+23y=18x+6\begin{cases} y = 6x + 2 \\ 3y = 18x + 6 \end{cases}

III. {y=6x+2y=6x+2\begin{cases} y = 6x + 2 \\ y = -6x + 2 \end{cases}

A.

I only

B.

II only

✓ Correct
C.

III only

D.

I and II only

Detailed Explanation

Choice B is correct. Choice B is the correct answer. System I: y=6x+2y = 6 x + 2 and y=6x5y = 6 x - 5 - Same slope (6), different intercepts (2 and -5) - Parallel lines → No solution System II: y=6x+2y = 6 x + 2 and 3y=18x+63y = 18 x + 6 - Divide second by 3: y=6x+2y = 6 x + 2 - Same line → Infinitely many solutions ✓ System III: y=6x+2y = 6 x + 2 and y=6x+2y = -6 x + 2 - Different slopes (6 and -6) - Intersecting lines → One solution Conclusion: Only System II has infinitely many solutions. Strategic Tip: For infinitely many solutions, equations must represent the exact same line (same slope, same intercept). Choice A is incorrect because System I has no solution (parallel lines). Choice C is incorrect because System III has one solution (different slopes). Choice D is incorrect because System I has no solution.

Key Steps:

The correct answer is II only

Why others are wrong:
A: Choice A is incorrect and may result from a calculation error.
C: Choice C is incorrect and may result from a calculation error.
D: Choice D is incorrect and may result from a calculation error.

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