Question

CM : a(2a -3) -2a(a +1) chia hết cho 5

Answer 1

Ta có : \(a\left(2a-3\right)-2a\left(a+1\right)\)

           \(=a.2a-a.3-2a.a-2a.1\)

           \(=2a^2-3a-2a^2-2a\)

           \(=-5a⋮5\) ( vì \(-5⋮\forall\) )

\(\Rightarrow a\left(2a-3\right)-2a\left(a+1\right)⋮5\)

Answer 2

Ta có : 

\(a\left(2a-3\right)-2a\left(a+1\right)\\ =a.2a-a.3-2a.a-2a.1\\ =2a^2-3a-2a^2-2a\\ =-5a:a\)

\(=>a\left(2a-3\right)-2a\left(a+1\right)⋮5\)