Multiple choice

In a series of positive numbers, t𝑛+1 + t𝑛 = S, t𝑛+1οΉ£t𝑛 = D and t𝑛+2 = t𝑛+1 + SοΉ£D, where 𝑛 is a natural number. If t1 = 2 and t2 = 4, then find the sum of the first ten terms of the series.

  1. 1440

  2. 1023

  3. 1257

  4. None of the above

Reveal answer Fill a bubble to check yourself
B Correct answer
AI explanation

Using the first two terms, the common sum S is 2 plus 4, which equals 6, and the common difference D is 4 minus 2, which equals 2. The next term is found by adding the previous term to S minus D, meaning we add 6 minus 2, or 4, to each preceding term. This makes the series 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, which is a geometric progression with a first term of 2 and a common ratio of 2. The sum of the first ten terms of this progression is 2 multiplied by (2^10 minus 1), which gives a total of 1023.