Делим население на площадь и получаем население одного км²
2,2*10⁷чел/7,7*10⁶ км²=2,2*10 чел/7,7км²=22чел/7,7км²=2,86чел/км²
![\left \{ {{ a_{3}=-7 } \atop { a_{2}+ a_{7} =13 }} \right.\\\\ \left \{ {{ a_{1}+2d=-7 } \atop { a_{1}+d+ a_{1} +6d=13 }} \right. \\\\ \left \{ {{ a_{1}+2d=-7 } \atop {2a _{1}+7d=13 }} \right. \\\\- \left \{ {{2a _{1} +4d=-14} \atop {2a _{1}+7d=13 }} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7B+a_%7B3%7D%3D-7+%7D+%5Catop+%7B+a_%7B2%7D%2B+a_%7B7%7D+%3D13+%7D%7D+%5Cright.%5C%5C%5C%5C+%5Cleft+%5C%7B+%7B%7B+a_%7B1%7D%2B2d%3D-7+%7D+%5Catop+%7B+a_%7B1%7D%2Bd%2B+a_%7B1%7D+%2B6d%3D13+%7D%7D+%5Cright.+%5C%5C%5C%5C+%5Cleft+%5C%7B+%7B%7B+a_%7B1%7D%2B2d%3D-7+%7D+%5Catop+%7B2a+_%7B1%7D%2B7d%3D13+%7D%7D+%5Cright.+%5C%5C%5C%5C-+%5Cleft+%5C%7B+%7B%7B2a+_%7B1%7D+%2B4d%3D-14%7D+%5Catop+%7B2a+_%7B1%7D%2B7d%3D13+%7D%7D+%5Cright.++)
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- 3d = - 27
d = 9
a₁ = - 7 - 2d = - 7 - 2 * 9 = - 7 - 18 = - 25
<span>2(a+1)(b+1)=(a+b)(а +b +2)
2(ab+a+b+1)=a</span>²+ab+2a+ab+b²+2b
2ab+2a+2b+1=a²+2ab+2a+b²+2b
a²+b²=1
6.
![x^{2} +2x +q =0 \\ ](https://tex.z-dn.net/?f=+x%5E%7B2%7D+%2B2x+%2Bq+%3D0+%5C%5C+%0A)
Пусть х1 и х2 - корни, тогда по теореме Виета
![x_{1} + x_{2} = -2 \\ x_{1} x_{2} =q \\ ](https://tex.z-dn.net/?f=+x_%7B1%7D+%2B++x_%7B2%7D+%3D+-2+%5C%5C+%0A+x_%7B1%7D++x_%7B2%7D+%3Dq+%5C%5C+%0A)
и по условию
![\frac{ x_{1} }{ x_{2} } = 6 => x_{1} = 6 x_{2} \\](https://tex.z-dn.net/?f=+%5Cfrac%7B+x_%7B1%7D+%7D%7B+x_%7B2%7D+%7D+%3D+6+%3D%3E+x_%7B1%7D+%3D+6+x_%7B2%7D++%5C%5C+)
Тогда
![x_{1} + x_{2} = -2 \\ 6 x_{2} + x_{2} = -2 \\ 7x_{2} = -2 \\ x_{2} = - \frac{2}{7} => x_{1} = 6 * (- \frac{2}{7} )= - \frac{12}{7}= -1 \frac{5}{7}\\ q = x_{1} x_{2} = (-1 \frac{5}{7})*(- \frac{2}{7} ) = \frac{12}{7}*\frac{2}{7}=\frac{24}{49} ](https://tex.z-dn.net/?f=x_%7B1%7D+%2B+x_%7B2%7D+%3D+-2+%5C%5C+%0A6+x_%7B2%7D++%2B+x_%7B2%7D+%3D+-2+%5C%5C+%0A7x_%7B2%7D+%3D+-2+%5C%5C+%0Ax_%7B2%7D+%3D+-++%5Cfrac%7B2%7D%7B7%7D+++%3D%3E+x_%7B1%7D+%3D+6+%2A+%28-++%5Cfrac%7B2%7D%7B7%7D+%29%3D+-++%5Cfrac%7B12%7D%7B7%7D%3D+-1+%5Cfrac%7B5%7D%7B7%7D%5C%5C+%0Aq+%3D+x_%7B1%7D+x_%7B2%7D+%3D+%28-1+%5Cfrac%7B5%7D%7B7%7D%29%2A%28-++%5Cfrac%7B2%7D%7B7%7D+%29+%3D+%5Cfrac%7B12%7D%7B7%7D%2A%5Cfrac%7B2%7D%7B7%7D%3D%5Cfrac%7B24%7D%7B49%7D%0A)
Объяснение:
1) 24х² + x + 1=0
D = b² - 4ac = 1² - 4·24·1.
Сразу видно что D <0. Следовательно, корней нет.
2) x² + 13x + 42 = 0
D = 13² - 4 · 1 · 42 = 169 - 168 = 1.
![x_{1,2}=\frac{-b\pm\sqrt{D}}{2a}=\frac{-13\pm1}{2}](https://tex.z-dn.net/?f=x_%7B1%2C2%7D%3D%5Cfrac%7B-b%5Cpm%5Csqrt%7BD%7D%7D%7B2a%7D%3D%5Cfrac%7B-13%5Cpm1%7D%7B2%7D)
![x_1=\frac{-13-1}{2}=-\frac{14}{2}=-7,\\x_2=\frac{-13+1}{2}=-\frac{12}{2}=-6.](https://tex.z-dn.net/?f=x_1%3D%5Cfrac%7B-13-1%7D%7B2%7D%3D-%5Cfrac%7B14%7D%7B2%7D%3D-7%2C%5C%5Cx_2%3D%5Cfrac%7B-13%2B1%7D%7B2%7D%3D-%5Cfrac%7B12%7D%7B2%7D%3D-6.)