解答
化简 (1+i)20
解答
−1024
求解步骤
(1+i)20
使用二项式定理: (a+b)n=i=0∑n(in)a(n−i)bia=1,b=i
=i=0∑20(i20)⋅1(20−i)ii
展开求和
=0!(20−0)!20!⋅120i0+1!(20−1)!20!⋅119i1+2!(20−2)!20!⋅118i2+3!(20−3)!20!⋅117i3+4!(20−4)!20!⋅116i4+5!(20−5)!20!⋅115i5+6!(20−6)!20!⋅114i6+7!(20−7)!20!⋅113i7+8!(20−8)!20!⋅112i8+9!(20−9)!20!⋅111i9+10!(20−10)!20!⋅110i10+11!(20−11)!20!⋅19i11+12!(20−12)!20!⋅18i12+13!(20−13)!20!⋅17i13+14!(20−14)!20!⋅16i14+15!(20−15)!20!⋅15i15+16!(20−16)!20!⋅14i16+17!(20−17)!20!⋅13i17+18!(20−18)!20!⋅12i18+19!(20−19)!20!⋅11i19+20!(20−20)!20!⋅10i20
化简 0!(20−0)!20!⋅120i0:1
化简 1!(20−1)!20!⋅119i1:20i
化简 2!(20−2)!20!⋅118i2:190i2
化简 3!(20−3)!20!⋅117i3:1140i3
化简 4!(20−4)!20!⋅116i4:4845i4
化简 5!(20−5)!20!⋅115i5:15504i5
化简 6!(20−6)!20!⋅114i6:38760i6
化简 7!(20−7)!20!⋅113i7:77520i7
化简 8!(20−8)!20!⋅112i8:125970i8
化简 9!(20−9)!20!⋅111i9:167960i9
化简 10!(20−10)!20!⋅110i10:184756i10
化简 11!(20−11)!20!⋅19i11:167960i11
化简 12!(20−12)!20!⋅18i12:125970i12
化简 13!(20−13)!20!⋅17i13:77520i13
化简 14!(20−14)!20!⋅16i14:38760i14
化简 15!(20−15)!20!⋅15i15:15504i15
化简 16!(20−16)!20!⋅14i16:4845i16
化简 17!(20−17)!20!⋅13i17:1140i17
化简 18!(20−18)!20!⋅12i18:190i18
化简 19!(20−19)!20!⋅11i19:20i19
化简 20!(20−20)!20!⋅10i20:i20
=1+20i+190i2+1140i3+4845i4+15504i5+38760i6+77520i7+125970i8+167960i9+184756i10+167960i11+125970i12+77520i13+38760i14+15504i15+4845i16+1140i17+190i18+20i19+i20
化简 1+20i+190i2+1140i3+4845i4+15504i5+38760i6+77520i7+125970i8+167960i9+184756i10+167960i11+125970i12+77520i13+38760i14+15504i15+4845i16+1140i17+190i18+20i19+i20:−1024
=−1024