Question

the sum of first 20 terms of an A.P. is 400 and sum of first 40 terms with ful explain​

Answer 1

Answer:

is your answer

mark me as brainlist

Answer 2

Step-by-step explanation:

S20 = 400

400 = 20/2(2a + (20 - 1)d)

40 = 2a + 19d

so by hit and trial method we can say that a is 1 and d is 2

so,

S40 = 20(2 + 39*2)

= 20( 80)

= 1600