Вправи: 76

76. Спростіть вираз:

1) 5n-120n – 7n-820n – 8n+720n = 5n-1- 7n-8- (8n+7)20n = 5n-1-7n+8-8n-720n = -10n20n = –12;

2) 9m+2m2- 4 – m-94- m2 + 1-7mm2- 4 = 9m+2m2- 4 + m-9m2- 4 + 1-7mm2- 4 = 9m+2+ m-9+ (1-7m)m2- 4 = 9m+2+m-9+1-7mm2- 4 = 3m-6m2- 4 = 3(m-2)m-2(m+2) = 3m+2;

3) 3kk3- 1 + 4k+11- k3 + k21- k3 = 3kk3- 1 – 4k+1k3- 1 – k2k3- 1 = 3k-4k+1- k2k3- 1 = 3k-4k-1- k2k3- 1 = -k-1- k2k3- 1 = -(k2+ k+1)k-1(k2+ k+1) = –1k-1 = 11-k.