1) (а-b)(a+b)/(a-b)(a+b)-(a+b)=(a-b)(a+b)/(a+b)(a-b-1)=a-b/a-b-1
2) a^2(5a+b)+b^2(5a+b)/5a+b^2=(a^2+b^2)(5a+b)/b(5a+b)=a^2+b^2/b
3) x^2+6x-x-6/x^2+6x-2x-12=x(x+6)-(x+6)/x(x+6)-2(x+6)=(x+6)(x-1)/(x-6)(x-2)=x-1/x-2
4) (1-c)(1+c)/c(c^2+2c+1)=(1-c)(1+c)/c(c+1)^2=1-c/c^2+c