Question

find the sum of first to terms 이
arithmete series 5 to +15 t using
suitable formule​

Answer 1

Answer:

We know, Sum of n terms is S

n

=

2

n

[2a+(n−1)d]

a= First term =2

d= Common difference =7−2=5

n= number of terms =20

S

20

=

2

20

[2(2)+(20−1)5]

S

20

=10[4+95]

S

20

=10(99)

S

20

=990