几道初中数学分式化简题（有图）

7.(a-b)(a+5b)/(a-b)=a+5b (a-2)(a-3)/(a-4)(a-3)=(a-2)/(a-4)
10 (4y^2-6y^2+y^2)/(8y^2-2y^2+8y^2)=-y^2/-2y^2=1/2
11.a(a+b)/(a+b)(a-4b)=a/(a+4b) =-1
12.
x/2=y/3=4/z=t
x=2t y=3t z=4t
(xy+yz+zx)/(x^2+y^2+z^2)
=[6t^2+12t^2+8t^2]/(4t^2+9t^2+16t^2)
=26/29