Explanation

Given sequence: -8, -5, -2, ..., 7

We have:

a = -8 (first term)

d = 3 (common difference)

Let 7 be the nth term

Using the formula: tn = a + (n - 1) d

7 = -8 + (n - 1) 3

Solving for n:

15 ÷ 3 = n - 1

n = 6

Now we have:

a = -8

d = 3

n = 6

Substituting these values in the formula for sum:

S₆ = (6/2) × [2 × (-8) + (6 - 1) × 3]

= (6/2) × [-16 + 15]

= 3 × -1

= -3

Therefore, the sum of the given sequence is -3.