首页 > 留学知识库

问题: f(x)=2x^2/(1+x^2),n∈Z+,则f(1)+f(2)+f(3)+...+f(n)+f(1/2)+f(1/3)+...+f(1/n)=____

f(x)=2x^2/(1+x^2),n∈Z+,则f(1)+f(2)+f(3)+...+f(n)+f(1/2)+f(1/3)+...+f(1/n)=_____

解答:

f(x)=2x²/(1+x²),n∈Z+,则f(1)+f(2)+...+f(n)+f(1/2)+f(1/3)+...+f(1/n)=?

f(x) = 2x²/(1+x²)
f(1/x) = (2/x²)/(1+1/x²) = 2/(x²+1)
--->f(x)+f(1/x) = (2x²+2)/(x²+1) = 2

f(1)+f(2)+...+f(n)+f(1/2)+f(1/3)+...+f(1/n)
=f(1)+[f(2)+f(1/2)]+[f(3)+f(1/3)]+...+[f(n)+f(1/n)]
=1 + 2(n-1)
=2n-1