求解几道GWD数学题~请指点

silengoal

1) the sumof the first K positive integers is equal to K(K+1)/2. what is the sum of the integers from n to m, inclusive, where 0<n<m?a. m(m+1)/2 - (n+1)(n+2)/2
b.m(m+1)/2 - n(n+1)/2
c. m(m+1)/2 - (n-1)n/2
d. (m-1)m/2- (n+1)(n+2)/2
e. (m-1)m/2 - n(n+1)/


红题字即是答案


2）If d=1/(2^3*5^7) is expressed as a terminating decimal, how many nonzero digits will d have?
a.1
b.2
c.3
d.7
e.10


谢谢大家解答~

silengoal

还有一个小疑问就是 在一个circle中 如果知道 arc (AB) 的长度和半径， 怎样求the length of AB segment?

dadadaxia

1、sum of the integers from n to m，就是n+(n+1)+....+m
也就是the sum of the first m positive integers 减去 the sum of the first (n-1) positive integers

2、d=1/(2^3*5^7)=(1/5^4)*(1/10)^3
(1/5^4)有2位非零digits

3、求弦角度，已知半径，就可以知道|AB|了

silengoal

明白了，谢谢了哦~~~