N=3
Bn=18
Sn=26
B₁-?
q-?
B₃=18
S₃=26
B₃=B₁*q²
B₁=<u> B₃ </u> = <u>18</u>
q² q²
S₃=<u>B₁(q³-1)</u>
q²(q-1)
26=<u> 18(q³-1)</u>
q-1
26=<u>18(q-1)(q²+q+1)</u>
q²(q-1)
26q²=18(q²+q+1)
13q²=9q²+9q+9
4q²-9q-9=0
D=81-4*4*(-9)=225
q₁=<u>9-15</u>=<u>-6</u>=<u>-3</u> - не подходит
8 8 4
q₂=<u>9+15</u> = <u>24 </u>=3
8 8
b₁=<u>18 </u>=2
3²
Ответ: b₁=2
q=3
<span>y = - 3tgx + 6x - 1,5П + 8 на отрезке [-П/3;П/3]
y`=-3/cos</span>²x+6=0
cos²x=1/2
(1+cos2x)/2=1/2
1+cos2x=1
cos2x=0
2x=π/2+πk
x=π/4+πk/2,k∈z
k=-1 x=-π/4∈[-π/3;π/3]
k=0 x=π/4∈[-π/3;π/3]
y(-π/3)=-3*(-√3)-2π-1,5π+8≈5-7,5+8=5,5 наибольшее
y(-π/4)=3-1,5π-1,5π+8≈11-9=2
y(π/4)=-3+1,5π-1,π+8=5
y(π/3)=-3√3+2π-1,5π+8≈4,4