20a²-8a+21a-28= 20a²+13a-28
-2b²+8b-6b²+21b= 29b-8b²
3x²-3x-5x²+10x= 7x-2x²
2a²-14a-3a²-6a+6a²-18= 5a²-29a-18
20a²-8a+21a-28= 20a²+13a-28
-2b²+8b-6b²+21b= 29b-8b²
3x²-3x-5x²+10x= 7x-2x²
2a²-14a-3a²-6a+6a²-18= 5a²-29a-18