3 Answers: Choice B, C, and D
Basically, everything except choice A.
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Explanation:
All exponential functions can be written into the form y = a*b^x
The b term determines if we have growth or decay.
If 0 < b < 1, then we have decay. If b > 1, then we have growth.
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For choice A, we have b = 1.7 which satisfies b > 1. This represents growth. So we cross choice A off the list.
Choice B looks almost identical since it appears b = 1.7 here as well, but note the negative exponent. It might help to rewrite choice B into y = 3( 1.7^(-2) )^x and note how b = (1.7)^(-2) = 0.346 approximately. This represents decay.
Choice C has b = 1/3 = 0.33 approximately which is also decay.
Finally, choice D has b = 2^(-1) = 1/(2^1) = 1/2 = 0.5 which is also decay.
Choices B through D have b values such that 0 < b < 1.
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Check out the graph below. It visually confirms the answers mentioned earlier. A growth function goes uphill as we move to the right, while a decay function moves downhill while moving to the right.
I used GeoGebra to make the graph.
