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Answer:
C.
Explanation:
For a graph to have a change in amplitude, there must be a coefficient in front of the equation, or the 'a' value.
Recall that the transformation form of a trigonometric graph is:
y = ±a(cos(b(x-h))+k
Where 'a' is the amplitude
'b' changes the period
'h' is a horizontal shift
'k' is a vertical shift
We can look at each choice and eliminate:
A. There is only a coefficient of -1 in front of the equation, which simply results in a reflection over the x-axis. This is incorrect.
B. This equation contains a b value of 2. This changes the period of the graph, not the amplitude. This is incorrect.
C. This equation contains a coefficient, or 'a' value of -2. The amplitude is changed by a factor of 2. This is correct.
D. This graph only contains a vertical shift of 1 unit up. This is incorrect.
Therefore, C is the correct answer.