해법
확장 (y2+y2)21
해법
y42+42y39+840y36+10640y33+95760y30+651168y27+3472896y24+14883840y21+52093440y18+150492160y15+361181184y12+722362368y9+1203937280y6+1666990080y3+1905131520+y31778122752+y61333592064+y9784465920+y12348651520+y15110100480+y1822020096+y212097152
솔루션 단계
(y2+y2)21
이항 정리 적용: (a+b)n=i=0∑n(in)a(n−i)bia=y2,b=y2
=i=0∑21(i21)(y2)(21−i)(y2)i
합계 확장
=0!(21−0)!21!(y2)21(y2)0+1!(21−1)!21!(y2)20(y2)1+2!(21−2)!21!(y2)19(y2)2+3!(21−3)!21!(y2)18(y2)3+4!(21−4)!21!(y2)17(y2)4+5!(21−5)!21!(y2)16(y2)5+6!(21−6)!21!(y2)15(y2)6+7!(21−7)!21!(y2)14(y2)7+8!(21−8)!21!(y2)13(y2)8+9!(21−9)!21!(y2)12(y2)9+10!(21−10)!21!(y2)11(y2)10+11!(21−11)!21!(y2)10(y2)11+12!(21−12)!21!(y2)9(y2)12+13!(21−13)!21!(y2)8(y2)13+14!(21−14)!21!(y2)7(y2)14+15!(21−15)!21!(y2)6(y2)15+16!(21−16)!21!(y2)5(y2)16+17!(21−17)!21!(y2)4(y2)17+18!(21−18)!21!(y2)3(y2)18+19!(21−19)!21!(y2)2(y2)19+20!(21−20)!21!(y2)1(y2)20+21!(21−21)!21!(y2)0(y2)21
0!(21−0)!21!(y2)21(y2)0간소화하다 :y42
1!(21−1)!21!(y2)20(y2)1간소화하다 :42y39
2!(21−2)!21!(y2)19(y2)2간소화하다 :840y36
3!(21−3)!21!(y2)18(y2)3간소화하다 :10640y33
4!(21−4)!21!(y2)17(y2)4간소화하다 :95760y30
5!(21−5)!21!(y2)16(y2)5간소화하다 :651168y27
6!(21−6)!21!(y2)15(y2)6간소화하다 :3472896y24
7!(21−7)!21!(y2)14(y2)7간소화하다 :14883840y21
8!(21−8)!21!(y2)13(y2)8간소화하다 :52093440y18
9!(21−9)!21!(y2)12(y2)9간소화하다 :150492160y15
10!(21−10)!21!(y2)11(y2)10간소화하다 :361181184y12
11!(21−11)!21!(y2)10(y2)11간소화하다 :722362368y9
12!(21−12)!21!(y2)9(y2)12간소화하다 :1203937280y6
13!(21−13)!21!(y2)8(y2)13간소화하다 :1666990080y3
14!(21−14)!21!(y2)7(y2)14간소화하다 :1905131520
15!(21−15)!21!(y2)6(y2)15간소화하다 :y31778122752
16!(21−16)!21!(y2)5(y2)16간소화하다 :y61333592064
17!(21−17)!21!(y2)4(y2)17간소화하다 :y9784465920
18!(21−18)!21!(y2)3(y2)18간소화하다 :y12348651520
19!(21−19)!21!(y2)2(y2)19간소화하다 :y15110100480
20!(21−20)!21!(y2)1(y2)20간소화하다 :y1822020096
21!(21−21)!21!(y2)0(y2)21간소화하다 :y212097152
=y42+42y39+840y36+10640y33+95760y30+651168y27+3472896y24+14883840y21+52093440y18+150492160y15+361181184y12+722362368y9+1203937280y6+1666990080y3+1905131520+y31778122752+y61333592064+y9784465920+y12348651520+y15110100480+y1822020096+y212097152