Question

if the first term of an appointment is -5and the common difference is 2,then the sum of the first 12terms is​

Answer 1

a = -5

d = 2

n = 12

S 12 = ?

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

S n = 12/2 [2(-5)+(12-1)2]

= 6 [ -10 + (11)2 ]

= 6 [ -10 + 22 ]

= 6 ( 12 )

= 72

Hence, the sum of first 12 terms is 72.