f(x)=1/x(x+1)=1/x-1/(x+1)
则f(1)+f(2)+...+f(n)
=1-1/2+1/2-1/3+...+1/n-1/(n+1)
=1-1/(n+1)
=n/(n+1)
=14/15
所以n=14
如果不懂,请追问,祝学习愉快!
f(x)=1/x(x+1)=1/x-1/(x+1)
则f(1)+f(2)+...+f(n)
=1-1/2+1/2-1/3+...+1/n-1/(n+1)
=1-1/(n+1)
=n/(n+1)
=14/15
所以n=14
如果不懂,请追问,祝学习愉快!