Đáp án: a) (x-1).(x-5)
Giải thích các bước giải: a) $x^{2}$ -6x+5
=$x^{2}$ -x-5x+5 =( $x^{2}$ -x)-(5x-5)
=x(x-1)-5(x-1) = (x-1 ).(x-5)
b) $x^{2}$ +8x+15 =$x^{2}$ + 5x +3x +15 = ($x^{2}$ +5x ) + (3x +15) = x(x+5) +3 (x+5)
=(x+3).(x+5)
c) $3x^{2}$ -16x+5 =$3x^{2}$ - 15x -x+5 =($3x^{2}$-15x) -(x-5) = 3x(x-5) - (x-5)
= (x-5) .(3x-1)
d) x4x4 - 7x27x2 +6 = x4x4 - $x^{2}$ -$6x^{2}$ +6 =( x4x4-$x^{2}$ ) - ($6x^{2}$ -6)
= $x^{2}$ ( $x^{2}$ -1)-6($x^{2}$ -1) =($x^{2}$-6).($x^{2}$ -1) = ($x^{2}$ -6).(x-1).(x+1)
e) 3x23x2 -8x+4 = $3x^{2}$ -6x -2x+4 =( $3x^{2}$-6x)-(2x-4) =3x(x-2)-2(x-2)=(x-2).(3x-2)
f/ 4x24x2 -4x-3= $4x^{2}$ +2x-6x+3=($4x^{2}$-2x)-(6x-3)= 2x(2x-1)-3(2x-1)=(2x-1).(2x-3)
