Question

Answer 1

đặt a=5k+3,b=5h+4

ab=(5k+3)(5h+4)=25kh+20k+15h+12 chia cho 5 dư 2

Answer 2

Đặt \(a=5k+3,b=5n+4\left(k,n\in N\right)\)

\(\Rightarrow ab=\left(5k+3\right)\left(5n+4\right)=25k^2+35k+12=5\left(5k^2+7k+2\right)+2\)chia 5 dư 2

Answer 3

\(a=5k+3\)

\(b=5c+4\)

\(ab=\left(5k+3\right)\left(5c+4\right)\)

\(=5kc+20k+15c+12\)

\(=5\left(kc+4k+3c+2\right)+2\) chia 5 dư 2(đpcm)

Answer 4

em cảm ơn