Вправи: 505

505. Спростіть вираз:

1) (9а – 2)(9а + 2) – 18а² = (9а)² – 2² – 18а² = 81а² – 4 – 18а² = 63a² – 4;

2) 25m² – (5m – 7)(5m + 7) – 25m² – ((5m)² – 7²) = 25m² – 25m² +

+ 49 = 49;

3) (b + 7)(b – 4) + (2b – 6)(2b + 6) = b² – 4b + 7b – 28 + (2b)² – 6² = b² + 3b – 28 + 4b² – 36 = 5b² + 3b – 64;

4) 4х(3х– 10y) – (4х + у)(4х – у) = 12х² – 40ху – ((4х)² – у²) = 12х²

– 40ху – 16х² + у² = –4х² – 40ху + у².