№2
a) (7y+4)/8y-(2y+3)/6y=(3(7y+4)-4(2y+3))/24y=(21y+12-8y-12)/24y=13/24y
b) a/(a+4)+a/(a-4)=(a^2-4a+a^2+4a)/(a+4)(a-4)=2a^2/a^2-16
№3
(x-10y^3)/2y+5y^2=(x-10y^3+10y^3)/2y=x/2y
При х=-18, у=4,5 получаем: -18/2*4,5=-1
№4
1+(2a-1)/a^2-2a+1-a/(a-1)=(a-1+2a-1-a)/(a-1)=2a-2/a-1=2(a-1)/a-1=2
№5
a) (b^3/63x^4)*(7x^4/b^12)=1/9b^9
b) (b+(5+b^2)/(2-b))*(4-4b+b^2)/2b+5=((2b-b^2+5+b^2)/2-b)*((b-2)/2b+5)=(2b+5/2-b)*(b-2/2b+5)=2-b/b-2