解答
展开 (x+x5)9
解答
x9+45x3+900x3+10500+x378750+x3393750+x51312500x+x62812500+x153515625+x91953125
求解步骤
(x+x5)9
使用二项式定理: (a+b)n=i=0∑n(in)a(n−i)bia=x,b=x5
=i=0∑9(i9)(x)(9−i)(x5)i
展开求和
=0!(9−0)!9!(x)9(x5)0+1!(9−1)!9!(x)8(x5)1+2!(9−2)!9!(x)7(x5)2+3!(9−3)!9!(x)6(x5)3+4!(9−4)!9!(x)5(x5)4+5!(9−5)!9!(x)4(x5)5+6!(9−6)!9!(x)3(x5)6+7!(9−7)!9!(x)2(x5)7+8!(9−8)!9!(x)1(x5)8+9!(9−9)!9!(x)0(x5)9
化简 0!(9−0)!9!(x)9(x5)0:(x)9
化简 1!(9−1)!9!(x)8(x5)1:45x3
化简 2!(9−2)!9!(x)7(x5)2:x2900(x)7
化简 3!(9−3)!9!(x)6(x5)3:10500
化简 4!(9−4)!9!(x)5(x5)4:x478750(x)5
化简 5!(9−5)!9!(x)4(x5)5:x3393750
化简 6!(9−6)!9!(x)3(x5)6:x61312500(x)3
化简 7!(9−7)!9!(x)2(x5)7:x62812500
化简 8!(9−8)!9!(x)1(x5)8:x2153515625
化简 9!(9−9)!9!(x)0(x5)9:x91953125
=(x)9+45x3+x2900(x)7+10500+x478750(x)5+x3393750+x61312500(x)3+x62812500+x2153515625+x91953125
化简 (x)9+45x3+x2900(x)7+10500+x478750(x)5+x3393750+x61312500(x)3+x62812500+x2153515625+x91953125:x29+45x3+900x23+10500+x2378750+x3393750+x51312500x+x62812500+x2153515625+x91953125
=x29+45x3+900x23+10500+x2378750+x3393750+x51312500x+x62812500+x2153515625+x91953125
化简 x29+45x3+900x23+10500+x2378750+x3393750+x51312500x+x62812500+x2153515625+x91953125:x9+45x3+900x3+10500+x378750+x3393750+x51312500x+x62812500+x153515625+x91953125
=x9+45x3+900x3+10500+x378750+x3393750+x51312500x+x62812500+x153515625+x91953125