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Let \((u_n)\) be the sequence defined by \(u_n=3 \cdot 2^n\) for \(n \ge 0\). Which method is
valid
to study its monotonicity, and what is the correct conclusion?
Use the ratio \(\dfrac{u_{n+1}}{u_n}\) and conclude that \((u_n)\) is decreasing.
Use the ratio \(\dfrac{u_{n+1}}{u_n}\) and conclude that \((u_n)\) is strictly increasing.
Use the difference \(u_{n+1}-u_n\) and conclude that \((u_n)\) is decreasing.
Use the difference \(u_{n+1}-u_n\) and conclude that \((u_n)\) is not monotonic.
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