# How do you find the partial sum of #Sigma 2n# from n=1 to 100?

##### 1 Answer

Feb 20, 2018

#### Answer:

# sum_(n=1)^100 \ 2n =10100 #

#### Explanation:

We seek the sum:

# S_100 = sum_(n=1)^100 \ 2n #

We can readily find the general sum:

# S_n = sum_(r=1)^n \ 2r #

# \ \ \ \ = 2 \ sum_(r=1)^n \ r #

And. we use the standard formula for the sum of the first

# sum_(r=1)^n \ r = 1/2n(n+1) #

Giving us:

# S_n = 2 * 1/2n(n+1) #

# \ \ \ \ = n(n+1) #

So with

# S_100 = 100(101) #

# \ \ \ \ \ \ \ = 10100 #