Решить)заранее 4с(с--4)^2 4ab+2(a-b)^2 3a(a--3)^2 (x-y)^2-x(x-2y) (a-3)(a-7)-2a(3a-5) 2c(3c+4)-3c(2c+1) (b+c)(b-c)-b(b-2c) a(a++b)(a-b) (y+10)(y-2)-4y(2-3y)

1.3а^2-6-а^2-6а+9

2.х^2-2хy+y-х^2+2хy

3.a^2-7a-3a-21-6c^2-3

1. 4c^2 - 8c - (c^2 -8c+16) =   4c^2 - 8c - c^2 + 8c -16 = 3c^2-16

2. 4ab + 2 ( a^2 - 2ab + b^2) = 4ab + 2a^2 - 4ab + 2b^2 =  2a^2  + 2b^2 = 2(a^2 + b ^2)

3. 3a^2 - 6a -( a^2 - 6a + 9) = 3a^2 - 6a -a^2  + 6a - 9 = 2a^2 - 9 

4. x^2 - 2xy + y^2 - x^2 + 2xy = y^2

5. a^2 - 7a - 3a + 21 - 6a^2 +  10a = - 5a^2 + 21

6. 6c^2 + 8c - 6c^2 - 3c = 5c

7. b^2 - c^2 - b^2 + 2cb = 2cb-2c^2

8. a^2- 5ba - a^2 + b^2 = b^2 - 5ba

9. y^2 - 2y + 10y - 20 - 8y + 12y^2 =  13y^2  - 20