Jawapan

2016-04-01T18:36:38+08:00
2016-04-02T09:05:55+08:00
4(a - l)² - 9
=4(a - l)(a - l) - 9
=4(a² - al - al + l²) - 9 
=4(a² - 2al + l²) - 9
=4a² - 8al + 4l² - 9