x²+7x-18=х²+9х-2х-18=х(х+9)-2(х+9)=(х+9)(х-2).
а) 5a(2 - a) + 6a(a - 7) = 10а - 5а² + 6а² - 42а = а² - 32а;
b) (b - 3)(b - 4)(b + 4)² = (b² - 4b - 3b + 12)(b² + 8b + 16) = (b² - 7b + 12)(b² + 8b + 16) = b⁴ + 8b³ + 16b² - 7b³ - 56b² - 112b + 12b² + 96b + 192 = b⁴ + b³ - 28b² - 16b + 192;
c) 20х + 5(х - 2)² = 20х + 5(х² - 4х + 4) = 20х + 5х² - 20х + 20 = 5х² + 20.
{x²+2x-9y²-6y=0⇒(x+1)²-(3y+1)²=0
{5x+6y+1=0
(x+1)²-(3y+1)²=0
(x+1)²=(3y+1)²
1)x+1=-3y-1
x=-3y-2
5(-3y-2)+6y+1=0
-15y-10+6y+1=0
-9y=9
y=-1
x=3-2=1
2)x+1=3y+1
x=3y
15y+6y+1=0
21y=-1
y=-1/21
x=-1/7
Ответ (1;-1);(-1/7;-1/21)
12(x-7)=7(x-2)
12x-84=7x-14
12x-84-7x+14=0
5x-70=0
5x=70
x=14