Question

find the sum of the first 20 terms of an arithmetic sequence with a first term of -14 and a comman difference of 4​

Answer 1

480

Explanation:

Sn = n÷2 × (2a + (n-1)d)

n = 20 a = -14 d = 4

S20 = 10 × (-28 + 19 × 4) = 480