Having had experience with some faulty proofs above, can you now answer the following questions
(a) From the equality (a−b)2=(m−n)2 may one draw the conclusion that a−b=m−n?
(b) For what value of x do the following expressions lose their meaning?
(1) x3−1x−1, (2) 1x2−1, (3) x+11−2x.
(c) If a>b, can one conclude that ac>bc for any number c?