i) x – 2y, 3x + 4y = (x – 2y) + (3x + 4y)
= (x + 3x) + (-2y + 4y) = 4x + 2y
ii) 4m2 – 7n2 + 5mn, 3m2 + 5n2 – 2mn
= (4m2 – 7n2 + 5mn) + (3m2 + 5n2 – 2mn)
= (4m2 + 3m2) + (-7n2 + 5n2) + (5mn – 2mn)
= 7 m2 + (-2n2) + 3mn = 7 m2 – 2n2 + 3mn
iii) 3a – 4b, 5c – 7a + 2b = (3a – 4b) + (5c – 7a + 2b)
= (3a – 7a) + (-4b + 2b) + 5c = -4a – 2b + 5c