Фармула дискриминантаD=b^2-4ас
D=25-16=9>0…значит 2 корня=
Ответ:
b1 =
Объяснение:
q=1/3
S5 = 27_2/3 = 83/3
b1 - ?
S = b1 * (q^(n) - 1 ) / (q-1)
S5 = b1 *(q^5 - 1) / (q - 1) = b1 * (1/243 - 1) / (-2/3) = - b1 * (-242/243) *3/2 =
= b1 * 121 / 81
83/3 = b1 * 121/81
b1 = 83 /3 : 121/81
b1 = 83/3 * 81/121
b1 = 83*27 / 121 = 2241 /121 = 18_63/121
Сos²2x + Cos6x - Sin²2x = 0
Cos4x + Cos6x = 0
2Cos5xCosx = 0
Cos5x = 0 или Cosx = 0
5x = π/2 + πk, k ∈Z x = π/2 + πn , n ∈Z
x = π/10 + πk/5, k ∈Z