Question

A. P. sum. solve if possible.

Answer 1

HELLO FRIEND

OPTION ( C ) n(n-1)/2 is the correct answer.

HERE'S HOW...



1 is logical and second one is with sum of AP series

1+1+1+1+1+1+….n time

see here you can se 1+1=2 (first two numbers)

2+1=3 (sum of first two numbers +third number)

so by going this way the last two terms will be

(n-1)+1=n

second way to do so,

sum of AP= n/2{a+l}……(n is number of terms, a is first number and l is last number)

so in the given equation (1+1+1+1…n terms)

sum,

=n/2{1+1}

=n/2{2}

=n

Answer 2

in AP it is clear that a =1 And d=1
we know that
n=n-1
$sum \: of \: n \: terms \: of \: an \: ap = \frac{n}{2} \:( a + (n - 1)d )\:$
so putting values
$\frac{n}{2} (1 + (n - 1 - 1)1)$
that is
$\frac{n}{2} (1 + n - 2) \\ \frac{n}{2} (n - 1)$
The answer is C