А) 6ab-3b² = 3b(2a-b)
Б) ac+bc-3a-3b = c(a+b)-3(a+b) = (c-3)(a+b)
=7(5+4√2)+7(5-4√2)/(5-4√2)(5+4√2)= 35+28√2+35-28√2/(5-4√2)(5+4√2)= 70/(5-4√2)(5+4√2)
3) Sтр = BC+AD/2 * √AB²-((AD-BC)²+AB²-CD²/2*(AD-BC))²
Sтр = 10+14/2 * √13²-((14-10)²+13²-15²/2*(14-10))² = 12 * √169-(16+169-225/8)² = 12*√144 = 12*12 = 144
Ответ: 144