\(A=\left[\left(x-1\right)\left(x-4\right)\right]\left[\left(x-2\right)\left(x-3\right)\right]+1=\left(x^2-5x+4\right)\left(x^2-5x+6\right)+1\)
\(=\left(x^2-5x+5-1\right)\left(x^2-5x+5+1\right)+1\)
\(=\left(x^2-5x+5\right)^2-1+1=\left(x^2-5x+5\right)^2\)
\(A=\left[\left(x-1\right)\left(x-4\right)\right]\left[\left(x-2\right)\left(x-3\right)\right]+1=\left(x^2-5x+4\right)\left(x^2-5x+6\right)+1\)
\(=\left(x^2-5x+5-1\right)\left(x^2-5x+5+1\right)+1=\left(x^2-5x+5\right)^2-1+1=\left(x^2-5x+5\right)^2\text{ laf scp}\)
A = ( x - 1 )( x - 2 )( x - 3 )( x - 4 ) + 1
= [ ( x - 1 )( x - 4 ) ][ ( x - 2 )( x - 3 ) ] + 1
= ( x2 - 5x + 4 )( x2 - 5x + 6 ) + 1
Đặt t = x2 - 5x + 5
A = ( t - 1 )( t + 1 ) + 1
= t2 - 1 + 1
= t2 = ( x2 - 5x + 5 )2
Cho ĐK x ∈ Z thì mới là một số chính phương --
