а) 6 ; б) 8 ; в) 8
Один кубик зовсім не зафарбований
20,7:0,9= 23 (праоагпнщр) прости
Из условия имеем
![b_7=-\frac{1}{6}=b_1\cdot q^6,\,b_5=-\frac{3}{4}=b_1\cdot q^4\rightarrow\frac{b_7}{b_5}=-\frac{1}{6}:\left(-\frac{3}{4}\right)=q^2](https://tex.z-dn.net/?f=b_7%3D-%5Cfrac%7B1%7D%7B6%7D%3Db_1%5Ccdot+q%5E6%2C%5C%2Cb_5%3D-%5Cfrac%7B3%7D%7B4%7D%3Db_1%5Ccdot+q%5E4%5Crightarrow%5Cfrac%7Bb_7%7D%7Bb_5%7D%3D-%5Cfrac%7B1%7D%7B6%7D%3A%5Cleft%28-%5Cfrac%7B3%7D%7B4%7D%5Cright%29%3Dq%5E2)
откуда
![q^2=\frac{2}{9}](https://tex.z-dn.net/?f=q%5E2%3D%5Cfrac%7B2%7D%7B9%7D)
поскольку все члены прогрессии отрицательны
![q\ \textgreater \ 0](https://tex.z-dn.net/?f=q%5C+%5Ctextgreater+%5C+0)
и
![q=\frac{\sqrt{2}}{3}\,\rightarrow b_4=\frac{b_5}{q}=-\frac{3}{4}\cdot\frac{3}{\sqrt{2}}=-\frac{9\sqrt{2}}{8}](https://tex.z-dn.net/?f=q%3D%5Cfrac%7B%5Csqrt%7B2%7D%7D%7B3%7D%5C%2C%5Crightarrow+b_4%3D%5Cfrac%7Bb_5%7D%7Bq%7D%3D-%5Cfrac%7B3%7D%7B4%7D%5Ccdot%5Cfrac%7B3%7D%7B%5Csqrt%7B2%7D%7D%3D-%5Cfrac%7B9%5Csqrt%7B2%7D%7D%7B8%7D)
100-18=82
1)10206*82/100=10206*0,82=8368,92
2)8*8368,92=66951,36
3)5*10206=51030
4)66951,36+51031=117981,36(руб)