Four Graph Options

6
advanced-math

Which graph correctly represents y=4(2)xy = 4(2)^{-x}?

A

Decreasing curve, y-intercept 4

B

Increasing curve, y-intercept 4

C

Decreasing curve, y-intercept 2

D

Increasing curve, y-intercept 2

Correct Answer: A

Choice A is the correct answer. Rewrite with a positive exponent.

  1. Rewrite: y=4(2)x=412x=4(0.5)xy = 4(2)^{-x} = 4 \cdot \frac{1}{2^x} = 4(0.5)^x.
  2. Initial Value: When x=0x=0, y=4y = 4.
  3. Direction: Base 0.5<10.5 < 1 means decay (decreasing).
  4. Match: Decreasing curve with y-intercept 4.

💡 Strategic Tip: Negative exponent flips the base: bx=(1b)xb^{-x} = (\frac{1}{b})^x.

Choice B is incorrect because negative exponent creates decay, not growth. Choice C is incorrect because the y-intercept is 4, not 2. Choice D is incorrect because both intercept and direction are wrong.