b1=b5/q^4 S10=b1(q^10-1)/q-1
b1=-9/-81 S10=1/9(-3^10-1)/-3-1
b1 =1/9 S10=1/9*(-59050)/-4
S10=-59050/9*(-1/4)
S10=59050/36
ОДЗ
x > 0
lg (x + 0,5) = lg 0,5/x
x + 0,5 = 0,5/x
x (x + 0,5) = 0,5
x^2 + 0,5x - 0,5 = 0 /*2
2x^2 + x - 1 = 0
D = 1 + 4*2 = 9
x1 = ( - 1 +3)/4 = 1/2 = 0,5
x2 = ( - 1 - 3)/4 = - 4/4 = - 1
Ответ
0,5
Sin2α=2sinαcosα
sinα=0.8, cos²α=1-sin²α=1-0.64=0.36, cosα=-0.6, π/2<α<π.
sin2α=2*0.8*(-0.6)=-0.96
Х
5+х
х(5+х)=66
х²+5х-66=0
Д=5²-4*(-66)=25+264=289=17²
х=(-5±17)/2
х1=-22/2=-11<0
х2=12/2=6
х=6
х+5=11
ответ 6 и 11