Read the formula "1 + 2 + 3 + 4 +..." 100 "is the sum of 100 consecutive natural numbers starting from 1 as follows It's inconvenient to write. For the sake of simplicity, we express it as ∑ (100 above, n = 1 below, and N on the right). Here the ∑ is the summation sign. Through reading the above materials, we can calculate ∑ {20 above, n = 1 below, and 1 / n (n + 1) on the right}? What does n (n + 1) mean? I don't understand it at all,

Read the formula "1 + 2 + 3 + 4 +..." 100 "is the sum of 100 consecutive natural numbers starting from 1 as follows It's inconvenient to write. For the sake of simplicity, we express it as ∑ (100 above, n = 1 below, and N on the right). Here the ∑ is the summation sign. Through reading the above materials, we can calculate ∑ {20 above, n = 1 below, and 1 / n (n + 1) on the right}? What does n (n + 1) mean? I don't understand it at all,

（1+100）×100÷2

The formula "1 + 2 + 3 +. + 100" represents the sum of 100 consecutive natural numbers starting from 1. Because the above formula is relatively long and inconvenient to write, we can
"1 + 2 + 3 +. + 100" means 100 / E / N = 1 / N. this "e" is a summation sign. For example, "1 + 3 + 5 +. + 99" (that is, the sum of continuous odd numbers within 100 from 1) can be expressed as 50 / E / N = 1 / (2n-1), and "the third power of 1 + the third power of 2 + the third power of 3 +. + the third power of 10" can be expressed as the third power of 10 / E / N = 1 / n,
2 + 4 + 6 + 8 +. + 100 is indicated by summation sign——
Calculate 5 / E / N = 1 / (quadratic power of n-1)=——

1.50/E/n=1/2n
2.1-1+4-1+9-1+16-1+25-1=50

Read: the formula "1 + 2 + 3 + 4 + 5 + "Plus 100" is the sum of 100 consecutive natural numbers starting from 1

5050 (1 + 100 multiplied by 50.. primary school students?