1.2a/a²-4 - 1/a-2; 2.(2a/b)² - a/b / b/2a; 3.x²/x+1 - 1/x+1 + 1; 4.(1/a+2 - 1/a-2) * a²-4/a.

1.2a/a²-4 - 1/a-2; 2.(2a/b)² - a/b / b/2a; 3.x²/x+1 - 1/x+1 + 1; 4.(1/a+2 - 1/a-2) * a²-4/a.
1.2a/a²-4 - 1/a-2; 2.(2a/b)² - a/b / b/2a; 3.x²/x+1 - 1/x+1 + 1; 4.(1/a+2 - 1/a-2) * a²-4/a.

1.2a/a²-4 - 1/a-2; 2.(2a/b)² - a/b / b/2a; 3.x²/x+1 - 1/x+1 + 1; 4.(1/a+2 - 1/a-2) * a²-4/a.
1 2a/a²-4 -1/a-2=2a/(a+2)(a-2) -1/(a-2)=2a/(a+2)(a-2) -（a+2)/(a+2)(a-2)
=（2a-a-2)/(a+2)(a-2)
=1/(a+2)
2 (2a/b)² -a/b /b/2a=4a²/b²-2a²/b²=2a²/b²
3 x²/x+1 -1/x+1+1=(x²-1)/(x+1)+1=(x+1)(x-1)/(x+1)+1=x
4 (1/a+2 -1/a-2)*a²-4/a=[(a-2)/(a+2)(a-2) -(a+2)/(a+2)(a-2）]*(a+2)(a-2)/a
=-4/(a+2)(a-2)*(a+2)(a-2)/a
=-4/a