Jawabanmu

2014-08-12T20:19:33+07:00
(x + 6)² - 2(x + 6) 
= x² + 2.6x + 6² - 2x - 12
= x² + 12x + 36 - 2x -12
= x² + 10x + 24

Isinya bukan 15
2014-08-12T20:20:28+07:00
(x + 6 )² - 2( x +6) = 15
⇔ (x²+12x+36)-(2x+12)=15
⇔x²+12x-2x+36-12=15
⇔x²+10x+24=15
⇔x²+10x+24-15=0
⇔ x²+10x+9=0
⇔ (x+9)(x+1)=0
jadi, x= -9 atau x= -1

semoga membantu :)