(5-a)/(a-5)=(5-a)/-(5-a)=-1
(10a-5a^2)/(14a-28)=5a(2-a)/-14(2-a)=-5a/14
(49-a^2)/(a-7)^2=-(a-7)(a+7)/(a-7)^2=-(a+7)/(a-7)
(x-5)^2/(50-2x^2)=(x-5)^2/(25-x^2)*2=(x-5)^2/(5^2-x^2)2=-(x-5)^2/(x+5)(x-5)2=-(x-5)/2*(x+5)