Question

Part 1- Make sure to show all work. Write both the (i) recursive formula and the (ii) explicit formula for the sequences

A) {-23,-15,-7,1,...}.
B) {5, 5.25, 5.50, 5.75,...}
Part 2- Calculate the 15th term in each of the above sequences, Use the Recursive method for one sequence and the Explicit formula for the other sequence. (make sure to label your work & show each step).

Answer 1

A) The sequence is {-23, -15, -7, 1,...}

The common difference of the sequence above, d = 8

The first term, a = -23

The number of terms, n = 15

The recursive formula is, aₙ = aₙ₋₁ + d

Using the recursive method gives;

a₅ = a₍₅₋₁₎ + d

Where;

a₍₅₋₁₎ = 1

Therefore, a₅ = 1 + 8 = 9, a₆ = 9 + 8 = 17, a₇ = 17 + 8 = 25, a₈ = 25 + 8 = 33, a₉ = 33 + 8 = 41, a₁₀ = 41 + 8 = 49, a₁₁ = 49 + 8 = 57, a₁₂ = 57 + 8 = 65 a₁₃ = 65 + 8 = 73, a₁₄ = 73 + 8 = 81, a₁₅ = 81 + 8 = 89

The 15th term of the sequence, {-23, -15, -7, 1,...}, a₁₅ = 89

We check by using explicit formula to get, aₙ = a + (n - 1)·d

Therefore

a₁₅ = -23 + (15 - 1)×8 = 89

B) The given sequence is B) {5 5.25, 5.50, 5.75,...}

The common difference, d = 0.25

The first term, a = 5

The required number of terms, n = 15

Using the recursive method gives;

a₅ = a₍₅₋₁₎ + d

Where;

a₍₅₋₁₎ = a₄ = 5.75

Therefore, a₅ = 5.75 + 0.25 = 6

a₆ = 6 + 0.25 = 6.25, a₇ = 6.25 + 0.25 = 6.5, a₈ = 6.5 + 0.25 = 6.75, a₉ = 6.75 + 0.25 = 7, a₁₀ = 7 + 0.25 = 7.25, a₁₁ = 7.25 + 0.25 = 7.5, a₁₂ = 7.5 + 0.25 = 7.75, a₁₃ = 7.75 + 0.25 = 8, a₁₄ = 8 + 0.25 = 8.25, a₁₅ = 8.25 + 0.25 = 8.5

The 15th term, of the sequence, {5 5.25, 5.50, 5.75,...}, a₁₅ = 8.5

We check by explicit formula to get, aₙ = a + (n - 1)·d

Therefore

a₁₅ = 5 + (15 - 1)×0.25 = 8.5

Explanation: