`a) 3x^2 - 16x + 5`
`= 3x^2 - 15x - x +5`
`= (3x^2 - 15x)- (x-5)`
`= 3x(x - 5) - 1(x-5)`
`= (3x-1)(x-5)`
`b)` Sửa `:`
`x^4 + 2x^2 - 3`
`= x^4 + 3x^2 - x^2 - 3`
`= (x^4 + 3x^2) - (x^2 +3)`
`= x^2(x^2 + 3) - 1(x^2 +3)`
`= (x^2 -1)(x^2 +3)`
`= (x^2 - 1^2)(x^2 +3)`
`= (x-1)(x+1)(x^2 +3)`
`c) (x^2 + x)^2 + 4(x^2 +x) - 12`
`= [(x^2 + x)^2 + 4(x^2 +x) + 4] - 16`
`= [(x^2 +x)^2 + 2 . (x^2 +x) . 2 + 2^2] - 4^2`
`= (x^2 + x +2)^2 - 4^2`
`= (x^2 + x + 2 -4)(x^2 + x + 2 + 4)`
`= (x^2 + x -2)(x^2 + x + 6)`
`= (x^2 + 2x - x - 2)(x^2 + x +6)`
`= [(x^2 +2x) - (x+2)](x^2 + x +6)`
`= [x(x+2) - 1(x+2)](x^2 + x +6)`
`= (x-1)(x+2)(x^2 + x +6)`
`#HPHG`