Question

if nth term of an ap is 2n-1 find the sum of first four terms​

Answer 1

Answer:

given that,

nth term=2n-1

so, put 1 in place of n

=2(1)-1

=2-1

=1

so we get first term

now we have to get second term

for common difference

so,

=2(2)-1

=4-1

=3

a2=3

now for d

a2-a1=d

3-1=2

2=d

now, s4=4/2(2×1+(4-1)2)

=2(2+(3)2)

=2(2+6)

=2(8)

=16 ans.