Question

Ajutor! Cele doua exercitii:

Answer 1

Răspuns:

7) 3; 8) 40

Explicație pas cu pas:

7.

$4 - \frac{1}{4} + \frac{1}{ {4}^{2} } - \frac{1}{ {4}^{3} } = \frac{ {4}^{4} - {4}^{2} + 4 - 1}{ {4}^{3} } = \\ = \frac{256 - 16 + 3}{64} = \frac{243}{64} = 3 \frac{51}{64}$

$\Big[4 - \frac{1}{4} + \frac{1}{ {4}^{2} } - \frac{1}{ {4}^{3} }\Big] = 3$

8.

$a_{1} = 10; \ r = 5$

$\boxed {a_{n} = a_{1} + (n - 1)\cdot r}$

$a_{7} = 10 + (7 - 1)\cdot 5 = 10 + 30 = 40$