Update fft.md

修复第n+1个点的点值表示法的typo

diff --git a/docs/math/poly/fft.md b/docs/math/poly/fft.md
index bc91260..d027566 100644 (file)
--- a/docs/math/poly/fft.md
+++ b/docs/math/poly/fft.md
@@ -85,7 +85,7 @@ $$
 $$
 
 $$
-f_n(x) = y_n = a_0 + a_1x_m+a_2x_m^2+a_3x_m^3+ \cdots + a_nx_m^n
+f_{n+1}(x) = y_{n+1} = a_0 + a_1x_{n+1}+a_2x_{n+1}^2+a_3x_{n+1}^3+ \cdots + a_nx_{n+1}^n
 $$
 
 一个非常通俗易懂的解释：