<span>5sin²x + cosx - 1 = 0</span>
5( 1 - cos²x) + cosx - 1 = 0
5 - 5cos<span>²x </span>+ cosx - 1 = 0
- 5cos²x + cosx + 4 = 0 /:(-1)
5cos²x - cosx - 4 = 0
(5cosx + 4)(cosx - 1) = 0
cosx = 1 ==> x = 2pik, k ∈ Z
cosx = - 0,8 ==> x = ± (pi - arccos(0,8)) + 2pik, k ∈ Z
<span><span><span>
</span></span></span><span>где, q ≠ 1
</span>165=(11-88*q)\(1-q)
(11-88q)/165=1-q
11/165-88/165q=1-q
q-88/165q=1-11/165
77/165q=154/165
q=154/165:77/165
q=154/165*165/77
q=154/77=2
<span>bn</span><span> = </span>b1<span> · </span>q^<span>n - 1</span><span>
</span>88=11*2^(n-1)
8=2^(n-1)
2³=2(n-1)
n-1=3
n=4
А=1,3*20 и это произведение делить на 39
Посчитайте сами:)