12
1)a-4ab/(a+b)+b=(a²+ab-4ab+ab+b²)/(a+b)=(a²-2ab+b²)/(a+b)=(a-b)²/(a=b)
2)a/(a+b)+b/(a-b)-2ab/(a-b)(a+b)=(a²-ab+ab+b²-2ab)/(a-b)(a+b)=
=(a²-2ab+b²)/(a-b)(a+b)=(a-b)²/(a-b)(a+b)=(a-b)/(a+b)
3)(a-b)²/(a+b):(a-b)/(a+b)=(a-b)²/(a+b)*(a+b)/(a-b)=a-b
4)a-b-a+b=0
16
1)1-(a+3b)/2a=(2a-a-3b)/2a=(a-3b)/2a
2)1/(a+3b)+1/(a-3b)=(a=3b+a+3b)/((a-3b)(a+3b)=2a/(a-3b)(a+3b)
3)(a-3b)/2a*2a/(a-3b)(a+3b)=1/(a+3b)
20
1)1-1/a=(a-1)/a
2)1+1/a=(a+1)/a
3)(a-1)/a:(a+1)/a=(a-1)/a*a/(a+1)=(a-1)/(a+1)