b1•(q^8–1) 81•(1/6561–1)
2. S8 = --------------- = ------------------- =
q–1 –2/3
1/81–81 -80•(-3) 40
= ----------- = ----------- = -----
-2/3 81•2 27
3. a1+3d+a1+5d=52
2a1+8d=52
a1+4d=26
a5=26
4. b1•q^3•b1•q^5=441
b1^2•q^8=441
b1•q^4=21
b5=21
5. q=b2:b1=-2/(5•2)=-1/5
b1 2 2•5 5
S = ------ = ------ = ------ = ----
1–q 6/5 6 3
6. b1•q^6=81
b1•q^2=625
q^4=81/625
q=3/5;
b1=81:729/15625=15625/9=1736 1/9
q=-3/5
b1=1736 1/9
44-30+40х=35х+14
40х-35х=14+30-44
5х=0
Х = 0
![x^{2} +14x-25=-4 x^{2} +35x-47 5 x^{2} -21x+22=0 ](https://tex.z-dn.net/?f=+x%5E%7B2%7D+%2B14x-25%3D-4+x%5E%7B2%7D+%2B35x-47%0A%0A5+x%5E%7B2%7D+-21x%2B22%3D0%0A)
D=b^2-4ac=441-4*5*22=441-440=1
x1=(21-1)/10=2
x2=(21+1)/2=2,2
ответ:2 и 2,2
= - 18С^2 - 6C - ( C^2 - 6C + 9) = - 18C^2 - 6C - C^2 + 6C - 9 = - 19C^2 - 9