2
algebra

For what value of kk does the system have no solution? {2x5y=104x10y=k\begin{cases} 2x - 5y = 10 \\ 4x - 10y = k \end{cases}

A

k=20k = 20

B

k=5k = 5

C

k=10k = 10

D

Any value except 20

Correct Answer: D

Choice D is the correct answer. For no solution, we need parallel lines (proportional coefficients but different constants).

Step 1: Notice the second equation's coefficients are double the first: 2(2x5y)=2(10)=202(2x - 5y) = 2(10) = 204x10y=204x - 10y = 20

Step 2: Analysis:

  • If k=20k = 20: equations are identical → infinitely many solutions
  • If k eq20k \ eq 20: equations have same left side but different right side → parallel lines → no solution

Conclusion: No solution for any value except 20.

💡 Strategic Tip: Parallel lines occur when left sides are proportional but right sides aren't.

Choice A is incorrect because k=20k = 20 gives infinitely many solutions, not no solution.

Choice B is incorrect because while k=5k = 5 gives no solution, it's not the only such value.

Choice C is incorrect because while k=10k = 10 gives no solution, it's not the only such value.