5
advanced-math

If 52x=255x5^{2x} = 25 \cdot 5^x, what is xx?

A

x=0x = 0

B

x=2x = 2

C

x=1x = 1

D

x=1x = -1

Correct Answer: B

Choice B is the correct answer. Rewrite with the same base and solve.

  1. Rewrite: 25=5225 = 5^2, so 255x=525x=5x+225 \cdot 5^x = 5^2 \cdot 5^x = 5^{x+2}.
  2. Equation: 52x=5x+25^{2x} = 5^{x+2}.
  3. Equal bases: Set exponents equal: 2x=x+22x = x + 2.
  4. Solve: 2xx=22x - x = 2, so x=2x = 2.
  5. Verify: 52(2)=54=6255^{2(2)} = 5^4 = 625 and 2552=2525=62525 \cdot 5^2 = 25 \cdot 25 = 625

💡 Strategic Tip: When bases are equal, set exponents equal to solve.

Choice A is incorrect because50=15^0 = 1 and 2550=2525 \cdot 5^0 = 25, not equal. Choice C is incorrect because52=255^2 = 25 and 255=12525 \cdot 5 = 125, not equal. Choice D is incorrect because52=0.045^{-2} = 0.04 and 2551=525 \cdot 5^{-1} = 5, not equal.