x^2-36/2x+12
=(x+6)(x-6)/2(x+6)
=1/2x-3
a2-2a+1/1-a
=(a+1)(a-1)/-(a+1)
=-(a-1)
=1-a
3x-4y/8xy-6x2
=(3x-4y)/-2x(3x-4y)
=1/2x