( 7 - 3X )^2 = 49 - 42X + 9X^2
-------------------------------------
( 6M - N )*( 6M + N ) = 36M^2 - N^2
---------------------------------------
42AB - ( 3A + 7B )^2 = 42AB - 9A^2 - 42AB - 49B^2 = - 9A^2 - 49B^2
---------------------------------------
( M - 5M )*( M + 5N ) + ( 5N - 1 )^2 = M^2 - 25N^2 + 25N^2 - 10N + 1 =
= M^2 - 10N + 1
-----------------------------------------