a) `x^4+64 =(x^2)^2 + 2.x^2 . 8 + 8^2 - 16x^2`
`= (x^2+8)^2-(4x)^2=(x^2+8+4x)(x^2+8-4x)`
b) `x^3 - 8-(x-2)(x-12) = (x^3-2^3) - 8(x-2)(x-12)`
`=(x-2)(x^2+2x+4)-8(x-2)(x-12)=(x-2)(x^2+2x+4-8x+96)`
`= (x-2)(x^2-4x+100)`
c) `x^2+5x+8 = (x^2+2.x. 5/2 + (5/2)^2) +32/5 = (x+5/2)^2 + 32/5`
`=>` Không phân tích được.