Jawapan

2015-09-04T23:58:29+08:00
2015-09-05T00:07:33+08:00
= x × x = x²
= x × -4 = -4x
= -5 × x = -5x
= -5 × -4 = 20

= x² - 4x - 5x + 20
= x² - 9x + 20