1) If we add - x to x² + 3 x we will get: x² + 3 x - x = x² + 2 x, with same number of terms and same degree (2),
2 ) xy - 1 + xy = 2 xy - 1
3 ) x + y - 3 y = x - 2 y
4 ) x³ - 5 x² + 1 - 2 x³ = - x³ - 5 x² + 1
Pairs :
( x² + 3 x) ↔ ( -x )
( xy - 1)↔ ( xy )
( x + y ) ↔ ( - 3 y )
( x³ - 5 x + 1 ) ↔ ( - 2 x³ )
