(i) x2 – (-5x2) = x2 + 5x2
= (1 + 5) x2
= (6)x2 = 6x2
(ii) (a + b) (a – b)
= a + b – a + b
= a – a + b + b
= (1 – 1)a + (1 + 1)b
= 0a + 2b = 2b
(iii) (4x2 – 3xy + 8) – (x2 + 5x + 4)
= 4x2 – 3xy + 8 – x2 – 5x – 4
= 4x2 – x2 – 3xy – 5x + 8 – 4
= (4 – 1)x2 – 3xy – 5x + 4
= 3x2 – 3xy – 5x + 4
(iv) (3xy – 2x2 – 2y2) – (5x2 – 7xy + 5y2)
= 3xy – 2x2 – 2y2 – 5x2 + 7xy – 5y2
= 3xy + 7xy – 2x2 – 5x2 – 2y2 – 5y2
= (3 + 7)xy + (-2 – 5)x2 + (-2 – 5)y2
= 10xy – 7x2 – 7y2
= -7x2 – 7y2 + 10xy
(v) (5p2 + 2q2 – pq2) – (4pq – 5q2 – 3p2)
= 5p2 + 2q2 – pq2 – 4pq +5q2 + 3p2
= 5p2 + 3p2 + 2q2 +5q2 – pq2 – 4pq
= (5 + 3)p2 + (2 + 5)q2 – pq2 – 4pq
= 8p2 + 7q2 – pq2 – 4pq
(vi) (5x – 10) – (x2 + 10x – 5)
= 5x -10 – x2 – 10x +5
= -x2 + 5x – 10x – 10 + 5
= -x2 + (5-10)x – 5
= -x2 – 5x – 5