(ii) 36x2−12x+1−25y2
(iii) x4+x2+1
(3 marks)
(i) (5x−1x)2+4(5x−1x)+4
=(5x−1x)2+2×(5x−1x)×2+22
=(5x−1x+2)2 (1 mark)
(ii) 36x2−12x+1−25y2
=(6x)2−2×6x×1+12−(5y)2
=(6x−1)2−(5y)2
={(6x−1)−5y}{(6x−1)+5y}
=(6x−1−5y)(6x−1+5y)
=(6x−5y−1)(6x+5y−1) (1 mark)
(iii) x4+x2+1=(x4+2x2+1)−x2
=(x2+1)2−x2=(x2+1−x)(x2+1+x)
=(x2−x+1)(x2+x+1) (1 mark)