a) 16x mũ 2 -24xy+9y mũ 2 b) 2ab – b mũ 2 + 49-a mũ 2

a) `16x^2 – 24xy + 9y^2 = (4x)^2 – 2.4x.3y + (3y)^2 = (4x-3y)^2`

b) `2ab-b^2+49-a^2 = 49 – (a^2-2ab+b^2)`

`= 7^2 – (a-b)^2 = (7+a-b)(7-a-b)`