Question

Pls answer 8th question (I) part.

Answer 1

Hey mate your answer is here......

There are two methods to solve this type Question......

(i).
First seven odd no are

1, 3 ,5 ,7, 9, 11, 13

Total no is =7

Method No1•

By Number system rule....

The sum of N nature odd no is=N*N

=============≠===≠≠===>7*7
======================>49
Second Method is....

First no=1

D=3-1=2

n=7

This is an A.P.

sn=n/2[2a+(n-1).D]

==>7/2[2*1+(7-1).2]

==>7/2[2+6*2]

==>7/2*14

==>7*7

==>49

Proved......

Part(ii).

First 11 odd nos are

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21

Total no=11

Method 1•

same type

sn=N*N

sn=11*11

Sn=121

Second method
a=1
d=2
n=11

sn=11/2[2+(11-1).2]

sn=11/2[2+10*2]

sn=11/2[22]

sn=121.

proved......

Thanks