[tex]\it \dfrac{..}{..}\ \ \ b_5=24;\ \ b_4=12\\ \\ \\ q=\dfrac{b_5}{b_4}=\dfrac{24}{12}=2\\ \\ \\ b_1=\dfrac{b_4}{q^3}=\dfrac{12}{2^3}=\dfrac{12^{(4}}{8}=\dfrac{3}{2}=1,5\\ \\ \\ b_{10}=b_5\cdot q^5=24\cdot2^5=24\cdot32=768\\ \\ \\ b_{20}=b_{10}\cdot q^{10}=768\cdot2^{10}=768\cdot1024=786432\\ \\ \\ S_{10}=b_1\cdot\dfrac{q^{10}-1}{q-1}=1,5\cdot\dfrac{2^{10}-1}{2-1}=1,5\cdot(1024-1)=1,5\cdot1023=1534,5[/tex]
