Ohne Titel

Seite 1

a₂ + a₅ = 17

a₁ + r + a₁ + 4r = 17

2a₁ + 5r = 17.

a₃ + a₇ = 26

a₁ + 2r + a₁ + 6r = 26

2a₁ + 8r = 26.

17 - 5r + 8r = 26

3r = 9

r = 3.

2a₁ = 17 - 5.3

2a₁ = 17 - 15

2a₁ = 2

a₁ = 1.

.

a₁₅ = 1 + (15 - 1).3

a₁₅ = 1 + 14.3

a₁₅ = 1 + 42

a₁₅ = 43.

S = (1 + 43).15/2

S = 44.15/2

S = 330.