a ) xy + 1 - x - y
= x ( y - 1 ) + 1 - y
= x ( y - 1 ) - ( y - 1 )
= ( x - 1 ) ( y - 1 )
b ) x2 + ab + ac + bx
= ( b + x )x + a( b + c )
= ( b + x )1x + 1a( b + c )
= ( b + x ) ( x + a ) ( b + c )
c ) ax + bx - cx + a + b - c
= ( a + b - c )x + a + b - c
= ( a + b - c )x + ( a + b - c )1
= ( a + b - c ) ( x + 1 )