中等MATH-EXPL-004
What is the 15th term of the arithmetic sequence 5, 8, 11, …?
A. 45
B. 42
C. 50
D. 47✓ 答案
解說
The common difference is 3, so T_15 = 5 + 14 × 3 = 47. Using 15 differences instead of 14 gives 50. The formula is a + (n − 1)d.
The common difference is 3, so T_15 = 5 + 14 × 3 = 47. Using 15 differences instead of 14 gives 50. The formula is a + (n − 1)d.