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Set 15: Exponential Functions (Advanced)

Explanation

Answer: A

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

A.

x=6x = 6

✓ Correct
B.

x=4x = 4

C.

x=8x = 8

D.

x=2x = 2

Detailed Explanation

Choice A is correct. 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^{2 x} = 2^{3(x-2)} = 2^{3 x-6}. 4. Equal bases: 2x=3x62x = 3 x - 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 because 44=2564^4 = 256 and 82=648^2 = 64, not equal. Choice C is incorrect because this gives different values. Choice D is incorrect because 42=164^2 = 16 and 80=18^0 = 1, not equal.

Key Steps:

The correct answer is x=6x = 6

Why others are wrong:
B: Choice B 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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