(6a-7)(7+6a)+(7-8a)(8+7a)=
(6а – 7)(7 + 6а) + (7 – 8а)(8 + 7а) = (6а – 7) × (6а + 7) + 56 + 49а – 64а – 56а² = 36а² – 49 + 56 + 49а – 64а – 56а² = – 20а² + 7 – 15а = – 20а² – 15а + 7
Решите задачу: