2. Which of the following is the general term for the sequence a, -a, a, -a, . . .? A. a(-1)^(n - 1) B. (-a)^n C. (-1)a^(n + 1)?
回答 (2)
2016-05-11 5:44 am
2.
T(1) = a = a(-1)⁰ = a(-1)¹⁻¹
T(2) = -a = a(-1)¹ = a(-1)²⁻¹
T(3) = a = a(-1)² = a(-1)³⁻¹
T(4) = -a = a(-1)³ = a(-1)⁴⁻¹
......
Hence, T(n) = a(-1)ⁿ⁻¹
...... The answer is : A. a(-1)ⁿ⁻¹
T(1) = a = a(-1)⁰ = a(-1)¹⁻¹
T(2) = -a = a(-1)¹ = a(-1)²⁻¹
T(3) = a = a(-1)² = a(-1)³⁻¹
T(4) = -a = a(-1)³ = a(-1)⁴⁻¹
......
Hence, T(n) = a(-1)ⁿ⁻¹
...... The answer is : A. a(-1)ⁿ⁻¹
2016-05-11 5:41 am
C is automatically not the answer, because all of the terms would be negative.
Your powers of a isn't increasing from the series you provided, which makes B not possible.
B would make a series of -a, a^2, -a^3, a^4...
A is the solution.
Your powers of a isn't increasing from the series you provided, which makes B not possible.
B would make a series of -a, a^2, -a^3, a^4...
A is the solution.
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