a maths

a² - b²
= (a+b)(a-b)
we already have (a+b)=6, so we need to find (a-b)
(a-b)²
= a² + b² - 2ab
= (a² + b² + 2ab) – 4ab
= (a+b)² - 4ab
= 36 – 16
= 20
(a-b) = ± |(20) = ±2 |5; {| = square root}

Therefore, a² - b²
= (a+b)(a-b)
= 6 (±2 |5)
= ±12 |5
(±12 times square root 5)

2007-08-30 16:11:04 補充：
The square root symbol cannot be displayed, so I used the symbol "|" to represent square root instead.

(a+b)^2-4ab
=36-16
=20