А) 2ab+4b/3a * 6a^2/a^2b-4b=2b(a+2) * 2a/b(a^2-4)=2b(a+2) * 2a/b(a+2)(a-2)=2b * 2a/a-2=4ab/a-2
б) m^2-n^2/3mn : m^2+2mn+n^2/6m^2n^2=m^2-n^2/3mn * 6m^2n^2/m^2+2mn+n^2=(m+n)(m-n) * 2mn/(m+n)^2=(m-n) * 2mn/m+n=2m^2-2mn^2/m+n
в) x^2-y^2/x^2 : (x+y/x)^2=(x+y)(x-y)/x^2 * (x/x+y)^2=x-y/x * (1/1)^2=x-y/x