А
(y-20)/4y+(5y-2)/y²=(y²-20y+20y-8)/4y²=(y²-8)/4y²
б
7/(a+5)-(7a-3)/a(a+5)=(7a-7a+3)/a(a+5)=3/a(a+5)
в
28b^6/c³ * c^5/84b^6=c²/3
г
3(x+2)/(x+3) *(x+3)(x-3)/(x-2)(x+2)=3(x-3)/(x-2)
д
1)a/(2a-b)+a/b=(ab+2a²-ab)/b(2a-b)=2a²/b(2a-b)
2)(2a-b)/a * 2a²/b(2a-b) =2a/b