29 Вычислите значение выражения при a = 3, a = -3, a = \frac{1}{3}: a) 3a³; б) -\frac{1}{9}a²; в) \frac{2}{3}a²; г) -\frac{1}{3}a³.

a) 3a³, при a = 3:

3 · 3³ = 3 · 27 = 81

при a = -3:

3 · (-3)³ = 3 · (-27) = -81

при a = $$\frac{1}{3}$$ :

3 · ( $$\frac{1}{3}$$ )³ = 3 · $$\frac{1}{27}$$ = $$\frac{1}{9}$$

Ответ: 81; -81; $$\frac{1}{9}$$

б) - $$\frac{1}{9}$$ a², при a = 3:

- $$\frac{1}{9}$$ · 3² = - $$\frac{1}{9}$$ · 9 = -1

при a = -3:

- $$\frac{1}{9}$$ · (-3)² = - $$\frac{1}{9}$$ · 9 = -1

при a = $$\frac{1}{3}$$ :

- $$\frac{1}{9}$$ · ( $$\frac{1}{3}$$ )² = - $$\frac{1}{9}$$ · $$\frac{1}{9}$$ = - $$\frac{1}{81}$$

Ответ: -1; -1; - $$\frac{1}{81}$$

в) $$\frac{2}{3}$$ a², при a = 3:

$$\frac{2}{3}$$ · 3² = $$\frac{2}{3}$$ · 9 = 6

при a = -3:

$$\frac{2}{3}$$ · (-3)² = $$\frac{2}{3}$$ · 9 = 6

при a = $$\frac{1}{3}$$ :

$$\frac{2}{3}$$ · ( $$\frac{1}{3}$$ )² = $$\frac{2}{3}$$ · $$\frac{1}{9}$$ = $$\frac{2}{27}$$

Ответ: 6; 6; $$\frac{2}{27}$$

г) - $$\frac{1}{3}$$ a³, при a = 3:

- $$\frac{1}{3}$$ · 3³ = - $$\frac{1}{3}$$ · 27 = -9

при a = -3:

- $$\frac{1}{3}$$ · (-3)³ = - $$\frac{1}{3}$$ · (-27) = 9

при a = $$\frac{1}{3}$$ :

- $$\frac{1}{3}$$ · ( $$\frac{1}{3}$$ )³ = - $$\frac{1}{3}$$ · $$\frac{1}{27}$$ = - $$\frac{1}{81}$$

Ответ: -9; 9; - $$\frac{1}{81}$$