a)x²+8x+7= x² +7x +x +7 = x(x+7) +(x+7)
= (x+7)(x+1)
b)x²-5x+6 = x² -2x- 3x +6= x(x-2) -3(x-2)
= (x-2)(x+3)
c)x²+3x-18 = x² +6x - 3x -18= x(x+6) -3(x+6)
= (x+6)(x-3)
d)3x²-16x+5 = 3x² -15x -x +5 = 3x( x-5) -(x-5)
= (x-5)(3x-1)
e)3x²+6xy+3y²-3z² = 3( x² +2xy +y² -z²) = 3[ (x+y)² -z²]
= 3(x+y -z)(x+y+z)
Chúc bạn học tốt ^^