Відповіді на вправи: 610

1) a₁ = 7; a₁₆ = 67.

d – ?

a₁₆ = a₁ + 15d;

15d = a₁₆ – a₁;

d = $\frac{a_{16}-a_1}{15}$ = $\frac{67-7}{15}$ = 4.

2) a₁ = –4; a₉ = 0.

d – ?

a₉ = a₁ + 8d;

8d = a₉ – a₁;

d = $\frac{a_9-a_1}{8}$ = $\frac{0+4}{8}$ = $\frac{1}{2}$.

3) a₁ = 0,5; a₇ = 6,5.

a₇ = a₁ + 6d;

6d = a₇ – a₁;

d = $\frac{a_7-a_1}{6}$ = $\frac{\mathrm{6,5}-\mathrm{0,5}}{6}$ = 1.

4) a₁ = –10; a₃₁ = –20;

d – ?

a₃₁ = a₁ + 30d;

30d = a₃₁ – a₁;

d = $\frac{a_{31}-a_1}{30}$ = $\frac{-20+10}{30}$ = –$\frac{1}{3}$.