Odpowiedź:
zad 14
(cos109° + sin19°)² = [cos(180° - 71°) + sin(90° - 19°)]² =
= (- cos71° + cos71°)² = 0² = 0
Odp: A
zad 15
Sn = 3n² - 2n
S₂ = 3 * 2² - 2 * 2 = 3 * 4 - 4 = 12 - 4 = 8
S₁ = 3 * 1² - 2 * 1 = 3 - 2 = 1
a₂ = S₃ - S₂ = 8 - 1 = 7
Odp: B
zad 16
a₃ = a₁ + 2r = 19
a₆ = a₁ + 5r = - 2
układ równań
a₁ + 2r = 19
a₁ + 5r = - 2
odejmujemy równania
a₁ - a₁ + 2r - 5r = 19 + 2
- 3r = 21
3r = - 21
r = - 7
a₁ + 2r = 19
a₁ + 2 * ( - 7) = 19
a₁ - 14 = 19
a₁ = 19 + 14 = 33
a₇ = a₁ + 6r = 33 + 6 * (- 7) = 33 - 42 = - 9
Odp: C
