Question

[Member lỗi thời :>>]

Giúp mình với :

Answer 1

[tran vinh]

\(\frac{41.42...81}{1.3...79}=\frac{42.44....81}{1.3....39}=\frac{2^{20}.21.22...40.81}{1.3...39}=\frac{2^{30}.11.12...20.81}{1.3...19}=\frac{2^{35}.6.7...10}{1.3.5.7.9}=\frac{2^{38}.3.4.5}{1.3.5}=240^{ }\)

\(\frac{2^{38}.3.4.5}{1.3.5}=2^{40}=\left(2^{20}\right)^2\)là số cp

suy ra C là số cp

Answer 2

[Hoàng Dương『ʈєɑɱ❖๖ۣۜƝƘ☆』]

Ta có:

C=41.42.43...79.80.811.3.5.7...77.79C=41.42.43...79.80.811.3.5.7...77.79

→C=1.2.3...80.811.2.3...401.3.5.7...77.79→C=1.2.3...80.811.2.3...401.3.5.7...77.79

→C=1.2.3...80.81.(2.4.6..80)1.2.3...40(2.4.6...80).1.3.5.7...77.79→C=1.2.3...80.81.(2.4.6..80)1.2.3...40(2.4.6...80).1.3.5.7...77.79

→C=1.2.3...80.81.240.(1.23...40)1.2.3...401.2.3...79.80→C=1.2.3...80.81.240.(1.23...40)1.2.3...401.2.3...79.80

→C=81.240→C=81.240

→C=92.(220)2→C=92.(220)2

→C=(9.220)2→C=(9.220)2

→C→C là số chính phương