(1-x)*[(1+x)^10]
x的5次幂项
1*C(10,5)x^5-x*C(10,4)x^4
=[C(10,5)-C(10,4)]x^5
即x的5次幂的系数是
C(10,5)-C(10,4)
=252-210
=42
[(1-x)(1+x)]十次幂
=(1-x^2)^10,没有5次幂项