5
algebra

For what value of kk does the system have infinitely many solutions? {4x+2y=82x+y=k\begin{cases} 4x + 2y = 8 \\ 2x + y = k \end{cases}

A

k=2k = 2

B

k=8k = 8

C

k=4k = 4

D

k=6k = 6

Correct Answer: C

Choice C is the correct answer. For infinitely many solutions, the second equation must be a multiple of the first (or vice versa).

Step 1: Notice that the first equation's coefficients are double the second:

  • First: 4x+2y=84x + 2y = 8
  • Second: 2x+y=k2x + y = k

Step 2: Divide the first equation by 2: 4x+2y2=82\frac{4x + 2y}{2} = \frac{8}{2}2x+y=42x + y = 4

Step 3: For the equations to be identical: k=4k = 4

With k=4k = 4, both equations represent the same line, giving infinitely many solutions.

💡 Strategic Tip: For infinitely many solutions, one equation must be a scalar multiple of the other (including the constant term).

Choice A is incorrect becausek=2k = 2 would make the lines parallel (no solution), not identical.

Choice B is incorrect becausek=8k = 8 would make the lines parallel (no solution).

Choice D is incorrect becausek=6k = 6 would make the lines parallel (no solution).