Question

ILL GIVE BRAINLIEST! PLEASE HELP I DONT UNDERSTAND!

Answer 1

Answer:

S₁₅ = 645

Step-by-step explanation:

The sum to n terms of an arithmetic sequence is

$S_{n}$ = $\frac{n}{2}$ [ 2a₁ + (n - 1)d ]

where a₁ is the first term and d the common difference

Using the nth term formula $a_{n}$ = 5n + 3 , then

a₁ = 5(1) + 3 = 5 + 3 = 8

a₂ = 5(2) + 3 = 10 + 3 = 13 , then

d = a₂ - a₁ = 13 - 8 = 5

Thus

S₁₅ = $\frac{15}{2}$ [ (2 × 8) + (14 × 5) ]

     = 7.5( 16 + 70)

     = 7.5 × 86

     = 645