Maths problem:how to do (b), thanks?

(a) 
x³ - 8
= x³ - 2³ 
= (x-2)(x²+2x+4) - - - -→ 《 a³ - b³ = (a-b)(a²+ab+b²) 》

(b)
x³ - 6x + 4
= (x³ - 8) + 8 - 6x + 4 -→{make up(x³ - 8),so that the result of (a) can be used
= (x³ - 8) - 6x + 12
= (x-2)(x²+2x+4) - 6(x - 2) - - - - -→ From the result of (a)
= (x-2)(x²+2x+4-6)
= (x-2)(x²+2x-2)

* 請記着, " Hence" 的意思是 "從(a)的結果去計算(b)" ! 

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