Question

without adding , find the following sum (I) first 20 odd numbers​

Answer 1

Answer:

20×20=400

hope this helps

Answer 2

Answer:

400

Step-by-step explanation:

1+3+5+7+9+...........

We can observe that it is an A.P.

here a=1 ; d=2 ; n=20

Tn=a+(n-1)d

T20=a+19d

=1+19×2

=1+38

=39

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

=20/2(1+39)=10×40=400

Answer is 400