Відповіді на вправи: 613

1) b₃ = 32 i b₅ = 44.

b₁ – ? d – ?

b₃ = b₁ + 2d;

b₅ = b₁ + 4d;

b₁ + 2d = 32 | • (–1);

b₁ + 4d = 44;

+ –b₁ – 2d = –32;

b₁ + 4d = 44;

2d = 12;

b₁ = 32 – 2d;

d = 6;

b₁ = 32 – 2 • 6;

d = 6;

b₁ = 20.

2) b₄ = –16; b₇ = 8.

b₁ – ? d – ?

b₄ = b₁ + 3d;

b₇ = b₁ + 6d;

b₁ + 3d = –16 | • (–1);

b₁ + 6d = 8;

+ –b₁ – 3d = 16;

b₁ + 6d = 8;

3d = 24;

b₁ = –16 – 3d;

d = 8;

b₁ = –16 – 3 • 8;

d = 8;

b₁ = –4.