1) a-2-a/a-1= -2/a-1
2)3y+7+y+15/4-y= 4y+22/4-y
3)(2a-3)^2-(a-6)^2/9a-27
(2a-3-(a-6))(2a-3+a-6)/9a-27
(a+3)(3a-9)/9a-27
(a+3)*3*(a-3)/9a-27
(a+3)*3*(a-3)/9a-27
(a+3)*3/9
a+3/3
4) 25-3x-(7x-x^2)/(x-5)^2
25-3x-7x+x^2/(x-5)^2
25-10x+x^2/(x-5)
(5-x)^2/(x-5)^2
(-9-5+x))^2/(x-5)^2
(-5+x)^2/(x-5)
(x-5)^2/(x-5)^2=1