5
advanced-math

If 4x=8x24^x = 8^{x-2}, what is xx?

A

x=6x = 6

B

x=4x = 4

C

x=8x = 8

D

x=2x = 2

Correct Answer: A

Choice A is the correct answer. Rewrite with base 2 and solve.

  1. Rewrite: 4=224 = 2^2 and 8=238 = 2^3.
  2. Substitute: (22)x=(23)x2(2^2)^x = (2^3)^{x-2}.
  3. Simplify: 22x=23(x2)=23x62^{2x} = 2^{3(x-2)} = 2^{3x-6}.
  4. Equal bases: 2x=3x62x = 3x - 6.
  5. Solve: x=6-x = -6, so x=6x = 6.
  6. Verify: 46=40964^6 = 4096 and 84=40968^4 = 4096

💡 Strategic Tip: Convert to a common base (usually smallest prime).

Choice B is incorrect because44=2564^4 = 256 and 82=648^2 = 64, not equal. Choice C is incorrect because this gives different values. Choice D is incorrect because42=164^2 = 16 and 80=18^0 = 1, not equal.