分类：教育/科学-学习帮助
问题：数学三点共线问题若A(m+1,n
若A(m+1,n-1,3).B(2m,n,m-2n).(m+3,n-3,9)三点共线，则m+n_____
回答：AB (3m+1,2n-1,m-2n+3)
BC (3m+3,2n-3,m-2n+9)
AB=kBC
3m+1=k(3m+3).......(1)
2n-1=k(2n-3).......(2)
m-2n+3=k(m-2n+9)...(3)
(1)/(2): 
(3m+1)(2n-3)=(3m+3)(2n-1)
2n+3m=0............(4)
(4)代入(2)/(3)
(-3m-1)/(m+3m+3)=(-3m-3)/(m+3m+9)
m=0 
n=0
m+n=0
A(1,-1,3)  B(0,0,0) C(3,-3,9)