Hi, This is perhaps the most rookie question to Mathematics that one could ask, but I have searched for information on the question and found only one source which contained an answer. The answer was that it is because otherwise we wouldn't know what the value of either of the factors is. I must therefore be confused. We know that 1×a=a, thus (x+1)(x+1)=1 if both of the factors equal 1. In this case, if we set x=0 then we have (0+1)(0+1)=1; 1×1=1, therefore our factor is 1. As far as I know, there is no other value of x which can yield a value of 1, so why do we set the equations equal to 0? Thanks for any help.