Question

find the sum of first 20 term of an ap 1 4 7 10 using formula​

Answer 1

here is your answer

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

Sn = 20/2 [ 2*1 + (20-1)]* 3

Sn = 10 {2+19]*3

Sn = 10* 21*3

Sn = 630

Answer 2

Answer:

S10= 5(2a+9d)

= 5(2+27)

=5×29=145