Question

Raspuns rapid !!!! Matematica clasa a 5a.

Exercitiu:
Aflati ultima cifra a numarului a=1+1×2+1×2×3+...+1×2×3×....×2019.

Answer 1

`U(1)=1\\U(1*2)=2\\U(1*2*3)=6\\U(1*2*3*4)=U(24)=4\\U(1*\boxed{2}*3*4*\boxed{5})=0 \text{ because of } 2*5=10\\U(1*\boxed{2}*3*4*\boxed{5}*6)=0 \text{ because of } 2*5=10\\....................\\....................\\U(1*\boxed{2}*3*4*\boxed{5}*6*...*2019)=0 \text{ because of } 2*5=10`

`\implies~U(1+1*2+1*2*3+1*2*3*4+...+1*2*3*....*2019)=\\=U(1+1*2+1*2*3+1*2*3*4) = ~~~\text{(The others terms have U = 0)}\\=U(1+2+6+24)=U(33)=\boxed{\bf3}`