Assignment method is to assign certain special values to some letters in algebraic expressions (or equations or function expressions), so as to achieve the purpose of solving problems easily. The assignment method actually embodies the transformation idea from general to special.

Assignment format: let x (which can be replaced by corresponding letters) = value (such as 0, 1,-1, etc.). )

Example: Known (1? X)7=a0+a 1x+a2x (square) +a3x (cubic)+. +a7x7 Power. What is the value of a 1+a3+a5+a7?

Analysis: Because the equation in the title holds for all X, we can make x= 1 and x=- 1 in the known equation, and get A0+A1+A2+A3+A4+A5+A6+A7 = 0, ① respectively.

A0-a1+A2-A3+A4-A5+A6-A7 = (-2) to the 7th power ②

From ① to ②, we get 2(a 1+a3+a5+a7)=-(-2)7, so we get a 1+a3+a5+a7=64.