1
y(y+1)/y²=(y+1)/y
a(a-2)/(a-2)(a+2)=a/(a+2)
2
3/a+(a-3)/(a+5)=(3a+15+a²-3a)/a(a+5)=(a²+15)/a(a+5)
2x²/(x-2)(x+2)-2x²/(x=2)=(2x²-2x²+4x)/(x²-4)=4x/(x²-4)
3
(y-3)²/(y-3)(y+3) * y(y+3)/10(y-3)=y/10=70/10=7
4
x/y=a⇒y=x/a
y/z=1/a⇒z=ya⇒z=x/a*a=x
x/z=x/x=1