If every pair from among the equations `x^2+a x+b c=0. x^2+b x+c a=0,a n dx 62+c x+a b=0` has a common root, then the sum of the three common roots is `-1//2(a+b+c)` the sum of the three common roots is `2(a+b+c)` the product of the three common roots is `a b c` the product of the three common roots is `a^2b^2c^2`