[tex]\it b_2q^2=b_4 \Rightarrow 6q^2=54|_{:6} \Rightarrow q^2=9 \Rightarrow q=3, deoarewce\ q>0\\ \\ b_1=b_2:q=6:3=2\\ \\ b_2=6\\ \\ b_3=b_2\cdot q=6\cdot3=18\\ \\ b_4=54[/tex]
[tex]\it S_4=b_1+b_2+b_3+b_4=2+6+18+54=80\\ \\ T_4=\dfrac{^{27)}1}{\ \ 2}+\dfrac{^{9)}1}{\ 6}+\dfrac{^{4)}1}{\ 18}+\dfrac{1}{54}=\dfrac{27+9+4+1}{54}=\dfrac{41}{54}[/tex]
