Знак V это корень квадратный
6 / V3 = ( 6V3 ) /( V3•V3 ) = 6V3 /3 = 2V3
-1 3/4 - 2 1/12=-1 9/12 - 2 1/12=-3 10/12=-3 5/6
Производительность первой бригады x, второй y, третьей z.
Учитавыя условия задачи, составим и решим систему уравнений:
![\begin{cases} \left(\frac1x+\frac1y\right)12=1\\ \left(\frac1y+\frac1z\right)10=1\\ \left(\frac1x+\frac1z\right)15=1 \end{cases}\Rightarrow \begin{cases} \frac1x=\frac1{12}-\frac1y\\ \frac1z=\frac1{10}-\frac1y\\ \left(\frac1{12}-\frac1y+\frac1{10}-\frac1y\right)15=1 \end{cases}\\ \left(\frac1{12}-\frac1y+\frac1{10}-\frac1y\right)15=1\\ \left(\frac{11}{60}-\frac2y\right)15=1\\ \frac{11}4-\frac{30}y=1\\ \frac{30}y=\frac{11}4-1=\frac74\\ \frac1y=\frac{7}{120}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D+%5Cleft%28%5Cfrac1x%2B%5Cfrac1y%5Cright%2912%3D1%5C%5C+%5Cleft%28%5Cfrac1y%2B%5Cfrac1z%5Cright%2910%3D1%5C%5C+%5Cleft%28%5Cfrac1x%2B%5Cfrac1z%5Cright%2915%3D1+%5Cend%7Bcases%7D%5CRightarrow+%5Cbegin%7Bcases%7D+%5Cfrac1x%3D%5Cfrac1%7B12%7D-%5Cfrac1y%5C%5C+%5Cfrac1z%3D%5Cfrac1%7B10%7D-%5Cfrac1y%5C%5C+%5Cleft%28%5Cfrac1%7B12%7D-%5Cfrac1y%2B%5Cfrac1%7B10%7D-%5Cfrac1y%5Cright%2915%3D1+%5Cend%7Bcases%7D%5C%5C+%5Cleft%28%5Cfrac1%7B12%7D-%5Cfrac1y%2B%5Cfrac1%7B10%7D-%5Cfrac1y%5Cright%2915%3D1%5C%5C+%5Cleft%28%5Cfrac%7B11%7D%7B60%7D-%5Cfrac2y%5Cright%2915%3D1%5C%5C+%5Cfrac%7B11%7D4-%5Cfrac%7B30%7Dy%3D1%5C%5C+%5Cfrac%7B30%7Dy%3D%5Cfrac%7B11%7D4-1%3D%5Cfrac74%5C%5C+%5Cfrac1y%3D%5Cfrac%7B7%7D%7B120%7D)
![\begin{cases} x=\frac{3}{120}\\ z=\frac5{120}\\ \frac1y=\frac{7}{120} \end{cases}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D+x%3D%5Cfrac%7B3%7D%7B120%7D%5C%5C+z%3D%5Cfrac5%7B120%7D%5C%5C+%5Cfrac1y%3D%5Cfrac%7B7%7D%7B120%7D+%5Cend%7Bcases%7D)
Тогда работая вместе они построят коттедж за
дней.
35:5=7(тетрадей)
7+35=42
Ответ: всего 42 тетради и открыток.