問這題的答案解析，看不懂，請問是有代入什麼既定公式嗎？
謝謝
For each integer n > 1,
let A(n) denote the sum of the integers
from 1 to n. For example,
A(100) = 1 + 2 + 3 + … + 100 = 5,050. What is the value of A(200)
A10,100
B15,050
C15,150
D20,100
E21,100
答案解析：
A(200)=A(100)+101+102……+200
=A（100）+A（100）+100*100
=2*5，050+10，000
=20,100