Answer
2.5
Work Step by Step
We know that if $A$ is a real number and $B\gt0$, then the graphs of $y=Asin(Bx)$ and $y=Acos(Bx)$ will have an amplitude of $|A|$.
Therefore, the amplitude of the graph of $y=2.5cos x$ is $|2.5|=2.5$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.