Question

Find the sum of the first 21 terms of the AP: 21, 28, 35, 42, 49, 56,......​

Answer 1

Answer:

here's your answer....

hope it will help you......

Answer 2

Answer:

hi.........

here's the answer

a = 21 : d = 28-21 = 7 ; n = 21

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

S = 21/2 ( 2 (21) + (21 - 1 ) 7 )

S = 21/2 ( 42 + (20) 7 )

S = 21/2 (42+140)

S = 21/2 (182)

S = 21(91)

S = 1911

#hope this helped u

Step-by-step explanation: