8 700 - 1 800 = 6 900 книг продали во второй день
24 500 - 8 700 - 6 900 = 8 900 книг продали в третий день
![\begin{cases}7^{x-1}+7^x+7^{x+1}>171(1)\\log_3\frac{1}{x}+log_3(x^2+3x-9)\leq log_3(x^2+3x+\frac{1}{x}-10)(2)\end{cases}\\\\\\1)7^{x-1}+7^x+7^{x+1}>171\\7^{x-1}(1+7+49)>171\\7^{x-1}>3\\x-1>log_73\\x>log_721](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D7%5E%7Bx-1%7D%2B7%5Ex%2B7%5E%7Bx%2B1%7D%3E171%281%29%5C%5Clog_3%5Cfrac%7B1%7D%7Bx%7D%2Blog_3%28x%5E2%2B3x-9%29%5Cleq+log_3%28x%5E2%2B3x%2B%5Cfrac%7B1%7D%7Bx%7D-10%29%282%29%5Cend%7Bcases%7D%5C%5C%5C%5C%5C%5C1%297%5E%7Bx-1%7D%2B7%5Ex%2B7%5E%7Bx%2B1%7D%3E171%5C%5C7%5E%7Bx-1%7D%281%2B7%2B49%29%3E171%5C%5C7%5E%7Bx-1%7D%3E3%5C%5Cx-1%3Elog_73%5C%5Cx%3Elog_721)
![2)log_3\frac{1}{x}+log_3(x^2+3x-9)\leq log_3(x^2+3x+\frac{1}{x}-10)\\log_3(x+3-\frac{9}{x})\leq log_3(x^2+3x+\frac{1}{x}-10)\\x+3-\frac{9}{x}\leq x^2+3x+\frac{1}{x}-10\\x^2+2x+\frac{10}{x}-13\geq0\\x^3+2x^2-13x+10\geq0](https://tex.z-dn.net/?f=2%29log_3%5Cfrac%7B1%7D%7Bx%7D%2Blog_3%28x%5E2%2B3x-9%29%5Cleq+log_3%28x%5E2%2B3x%2B%5Cfrac%7B1%7D%7Bx%7D-10%29%5C%5Clog_3%28x%2B3-%5Cfrac%7B9%7D%7Bx%7D%29%5Cleq+log_3%28x%5E2%2B3x%2B%5Cfrac%7B1%7D%7Bx%7D-10%29%5C%5Cx%2B3-%5Cfrac%7B9%7D%7Bx%7D%5Cleq+x%5E2%2B3x%2B%5Cfrac%7B1%7D%7Bx%7D-10%5C%5Cx%5E2%2B2x%2B%5Cfrac%7B10%7D%7Bx%7D-13%5Cgeq0%5C%5Cx%5E3%2B2x%5E2-13x%2B10%5Cgeq0)
Раскладываем на множители:
![x^3+2x^2-13x+10=(x-1)(x^2+3x-10)=(x-1)(x+5)(x-2)=\\=0\\x=1\ ;x=2\ ;x=-5](https://tex.z-dn.net/?f=x%5E3%2B2x%5E2-13x%2B10%3D%28x-1%29%28x%5E2%2B3x-10%29%3D%28x-1%29%28x%2B5%29%28x-2%29%3D%5C%5C%3D0%5C%5Cx%3D1%5C+%3Bx%3D2%5C+%3Bx%3D-5)
Проводим прямые:
log_7(21)=1,56
______________(log_7(21)/////////////=>x
_-__[-5]/////+///[1]____-___[2]//+//=>x
x=0
![OTBET:x\in [2;+\infty)](https://tex.z-dn.net/?f=OTBET%3Ax%5Cin+%5B2%3B%2B%5Cinfty%29)
Извини , а как мы сможем решить , если даже нету фото да и учебников много по математике 4 - х классов !?
1.18:3=6(астр)
ответ.на одной клумбе растёт 6 астр ,а на другой 12