若(2-x)^100=a0+a1x+a2x^2+……+a100x^100 求:
2个回答

(2-x)^100=a0+a1x+a2x^2+……+a100x^100

(1)

令x=1得:

(2-1)^100=a0+a1+a2+.+a100

即a0+a1+a2+.+a100=1 ①

(2)

令x=0得:(2-0)^100=a0

即a0=2^100

(3)

a0>0,a10,a30

脚码为偶数系数为正,脚码为奇数系数为负

∴|a0|+|a1|+|a2|+……+|a100|

=a0-a1+a2-a3+.-a99+a100

令x=-1得

a0-a1+a2-a3+.-a99+a100=3^100 ②

即|a0|+|a1|+|a2|+……+|a100|=3^100

(4)

①+②:

2(a0+a2+a4+……+a100)=1+3^100

∴a0+a2+a4+……+a100=(1+3^100)/2