Question

The first two terms of an arithmetic

series are -2 and 3. How many terms
needed for the Sum to be 306?
​

Answer 1

Number of term n = 12

Explanation:

Given:

a1 = -2

a2 = 3

Sum = 306

Find:

Number of term n

Computation:

d = a2 - a1

d = 3 - (-2)

d = 5

Sn = n/2[2a + (n-1)d]

306 = n/2[2(-2) + (n-1)5]

612 = n[-4 + 5n -5]

5n² - 9n - 612 = 0

Number of term n = 12