Question

If nth term of A.P is (2n+1),what is sum of first 5terms​

Answer 1

hey there..!!

given, nth term of AP= (2n+1).....(eq 1)

now, putting the value of n in eq1 as 1,we get

a1= 2+1=3. (i)

also,

a2= 2+1=5. (ii)

as well as,

a5=10+1=11.

from i and ii,

a2-a1=d=2

now,

sum of 5terms=

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

=(5/2) [2*3+(5-1)*2]

=(5/2). [6+ 4*2]

=(5/2). [6+8]

=(5/2). 14

= 5*7

=35...(answer)

hope it will help.!