Ответ:

1)(2-с)²-с(с+4)=4-4c+c²-c²-4c=4-8c => 4-8*0.5= 0

2)(8b-8)(8b+8)-8b(8b+8)=(8b+8)(8b-8-8b)=(8b+8)(-8)=-64b-64=-64(b+1)=-64*3.6=-230.4

3)(4-y)²-y(y+1)=16-8y+y²-y²-y=16-9y=16-9*(-1/9)=16+1=17

4)(5ab)/(5ab-8a²)=(5ab)/(a(5b-8a))=(5b)/(5b-8a)=(5*8)/(5*8-8*3)=40/(40-24)=40/16=5/2=2.5

5)(x-3):((x²-6x+9)/(x+3))=(x-3)*((x+3)/(x-3)²)=(x+3)/(x-3)=(-21+3)/(-21-3)=-18/-24=3/4=0.75

Фух..Устал это писать)

Удачи)