F.2 Maths x4`

1)
xy - 4x - 3y + 12
= (xy - 4x) -(3y - 12)
= x(y - 4) - 3(y - 4)
= (x - 3)(y - 4)


2)
L.S.
= (1/4)(x - 2)(x - 6)
= (1/4)(x² - 8x + 12)
= (x²/4) - 2x + 3
= (x²/4) - 2x + 4 - 1
= [(x/2)² - 2(x/2)(2) + (2)²] -1
= [(x/2) - 2]² - 1
= R.S.

Hence, it is an identity.


3)
(4x² + 9)(2x - 3)(2x + 3)
= (4x² + 9)[(2x)² - (3)²]
= (4x² + 9)(4x² - 9)
= (4x²)² - (9)²
= 16x⁴ - 81


4)
(ab - 5c)²
= (ab)² - 2(ab)(5c) + (5c)²
= a²b² - 10abc + 25c²

哈哈...你係咪「老爺子」的後人??