Ctg² 210° + ctg² 120° + tg² 135° = ctg²(180 + 30) + ctg²(90 + 30) + tg²(90 + 45)=
= ctg²30 + tg²30 + ctg²45 = (√3)² + (1/√3)² + 1 = 3 + 1/3 + 1 = (4)1/3
S1=b1(1-q^2k)/(1-q)
S2=b1(1-(q^2)^k)/(1-q^2)
b1*(1-q^2k)*(1-q^2)/(b1*(1-q)*(1-q^2k))=(1-q^2)/(1-q)=1+q
1+q=5
q=5-1=4
ответ q=4
Y=-100x^2 K(-3;-900)
x=-3 y=-900
-900=-100×(-3)^2
-900=-100×9
-900=-900
(15*1/2)^2-(9*2/3)^2=7,5^2-(18/3)^2=7,5^2-6^2=56,25-36=20,25
Решение на фото..................