(1)
(2x-1)^4=a4x^4+a3x^3+a2x^2+a1x+a0
put x=1
a4+a3+a2+a1+a0 = 1
(2)
a3=coef.of x^3
= -(4C3)(2)^3
= -32
a1=coef.of x
= -(4C1)2
= -8
a1+a3 = -8-32=-40什么是coef啊coef. = coefficient 系数那of 是什么？coef. of x^3x^3的系数