Răspuns:
7) 3; 8) 40
Explicație pas cu pas:
7.
[tex]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} \\ [/tex]
[tex]\Big[4 - \frac{1}{4} + \frac{1}{ {4}^{2} } - \frac{1}{ {4}^{3} }\Big] = 3 \\ [/tex]
8.
[tex]a_{1} = 10; \ r = 5[/tex]
[tex]\boxed {a_{n} = a_{1} + (n - 1)\cdot r}[/tex]
[tex]a_{7} = 10 + (7 - 1)\cdot 5 = 10 + 30 = 40 \\ [/tex]
