Question

[Juki trinh]

CMR:

a,Bieu thuc : n(2n-3)-2n(n+1) luon chia het cho 5 voi moi n la so nguyen

b,Bieu thuc (n-1 )(n+4) - (n-4) (n+1)

Answer 1

[Đoàn Đức Hà]

a) \(n\left(2n-3\right)-2n\left(n+1\right)=2n^2-3n-2n^2-2n=-5n⋮5\)với \(n\inℤ\)

b) \(\left(n-1\right)\left(n+4\right)-\left(n-4\right)\left(n+1\right)=n^2+3n-4-\left(n^2-3n-4\right)=6n\)