Sum of series:1+2+3+..........+n is(a) n(

1.	Sum of series:1+2+3+..........+n is(a) n(
Answer» Answer: Sum of series = n(n+1) / 2 Step-by-step explanation: We know that sum of n-terms is given by, $\boxed{S_{n} = \frac{n[2a + (n-1)d]}{2} }$ From the arithemetic progression given here, AP -----> 1, 2, 3, ............ n we get, First term = a = 1 COMMON difference = d = 1 PUTTING these VALUES in the equation of sum of n-terms we get ${S_{n} = \frac{n[2a + (n-1)d]}{2} }$ $S_{n} = \frac{n[21 + (n-1)1]}{2}$ $S_{n} = \frac{n(2+n-1)}{2}$ $S_{n} = \frac{n(n+1)}{2}$

Answer»

Answer:

Sum of series = n(n+1) / 2

Step-by-step explanation:

We know that sum of n-terms is given by,

$\boxed{S_{n} = \frac{n[2a + (n-1)d]}{2} }$