9

Set 17: Exponential Functions (Advanced)

Explanation

Answer: A

A graph of y=a(b)xy = a(b)^x passes through (1,12)(1, 12) and (3,108)(3, 108). Which could be the equation?

A.

y=4(3)xy = 4(3)^x

✓ Correct
B.

y=12(3)xy = 12(3)^x

C.

y=3(4)xy = 3(4)^x

D.

y=108(12)xy = 108(12)^x

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Find aa and bb from the points. 1. Point 1: 12=a(b)1=ab12= a(b)^1 = ab. 2. Point 2: 108=a(b)3=ab3108= a(b)^3 = ab^3. 3. Divide: 10812=b2=9\frac{108}{12} = b^2 = 9, so b=3b = 3. 4. Find aa: a(3)=12a(3) = 12, so a=4a = 4. 5. Verify: 4(3)1=124(3)^1 = 12 ✓, 4(3)3=1084(3)^3 = 108 ✓ Strategic Tip: Divide equations to eliminate aa and solve for bb first. Choice B is incorrect because at x=1x=1, this gives 12(3)=361212(3)=36 \neq 12. Choice C is incorrect because the base and coefficient are swapped. Choice D is incorrect because both values are from points, not the equation.

Key Steps:

The correct answer is y=4(3)xy = 4(3)^x

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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