a^2-9/a^2+6a+9/a-3/a^2+3a-a-a^2/a^2-1怎么化简

a^2-9/a^2+6a+9/a-3/a^2+3a-a-a^2/a^2-1怎么化简
a^2-9/a^2+6a+9/a-3/a^2+3a-a-a^2/a^2-1怎么化简

a^2-9/a^2+6a+9/a-3/a^2+3a-a-a^2/a^2-1怎么化简
原式=[(a+3)(a-3)/(a+3)²]*[a(a+3)/(a-3)]+a(a-1)/(a+1)(a-1)
=a+a/(a+1)
=(a²+2a)/(a+1)

4x+9y=12 (1)
3y-2z=1 (2)
4x+5z=19/4 (3)
(1)-(3)
9y-5z=29/4 (4)
(4)-(2)×3
-5z+6z=29/4-3
所以z=17/4
y=(2z+1)/3=19/6
x=(12-9y)/4=-33/8

太乱

a^2-12/a^2+9/a+8a-2