gia su p ; p + 4 ; p + 8 la ba so nguyen to
ta thay p khong bang 2 vi neu p = 2 thi p + 4 = 6 va p + 8 = 10
xep p = 3 thi 3 ; 17 ; 11 la bo ba nguyen to lien tiep co hieu bang 4
xet p > 3 thi p co dang 3k + 1 hoac 3k + 2 (k thuoc N) [ kien thuc ve nguyen to lon hon 3]
loai p = 3k + 1 vi khi do p + 8 = 3k + 1 +8 = 3k + 8 = 3k + 3 . 3 = 3 . (k + 3) chia het cho 3, la hop so
loai p = 3k + 2 vi khi do p + 4 = 3k + 2 + 4 = 3k + 6 = 3k + 3 . 2 = 3 . (k + 2) chia het cho 3, la hop so
vay chi co duy nhat 3; 7; 11 thoa man de bai
suy ra day la dieu can chung minh
ta thay p
toán lớp 1 mà cũng có toán chứng minh a
