4x^2-25=0
x^2=25/4
x=5/2
x=-5/2
<span>5x^3-125x=0
5x(x^2-25)=5x(x-5)(x+5)=0
x=0
x=-5
x=5
</span>
85% шахматистов это 17 человек.
1% от шахматистов 17:85=0.2человека.
100% шахматистов или 80% класса 0.2*100=20 человек.
20:80=0.25 человека - 1% от класса.
0.25*100=25 человек - всего в классе.
Спасибо поставить не зубудь)
5x+3(3x+7)=35
5x+9x+21=35
14x+21=35
14x=35-21
14x=14
x=1
Возможно показатель степени 2х+1. Ни 3, ни 5 не подходят в условие.
![25^{x+0,5}-7\cdot 10^{x}+2^{2x+1}\geq 0\\\\5^{2x+1}-7\cdot 5^{x}\cdot 2^{x}+2^{2x+1}\geq 0\\\\5\cdot 5^{2x}-7\cdot 5^{x}\cdot 2^{x}+2\cdot 2^{2x}\geq 0\; |:2^{2x}>0\\\\5\cdot (\frac{5}{2})^{2x}-7\cdot (\frac{5}{2})^{x}+2\geq 0\\\\t=(\frac{5}{2})^{x}>0\; \; ,\; \; \; \; 5t^2-7t+2\geq 0\; \; ,\; \; D=49-40=9\; ,\; \; t_{1,2}=\frac{7\pm 3}{10}\; ,\\\\t_1=\frac{2}{5}\; \; ,\; \; t_2=1\\\\5(t-\frac{2}{5})(t-1)\geq 0\; \; \; \; \; +++[\, \frac{2}{5}\, ]---[\, 1\, ]+++\\\\t\leq \frac{2}{5}\; \; \; ili\; \; \; t\geq 1](https://tex.z-dn.net/?f=25%5E%7Bx%2B0%2C5%7D-7%5Ccdot%2010%5E%7Bx%7D%2B2%5E%7B2x%2B1%7D%5Cgeq%200%5C%5C%5C%5C5%5E%7B2x%2B1%7D-7%5Ccdot%205%5E%7Bx%7D%5Ccdot%202%5E%7Bx%7D%2B2%5E%7B2x%2B1%7D%5Cgeq%200%5C%5C%5C%5C5%5Ccdot%205%5E%7B2x%7D-7%5Ccdot%205%5E%7Bx%7D%5Ccdot%202%5E%7Bx%7D%2B2%5Ccdot%202%5E%7B2x%7D%5Cgeq%200%5C%3B%20%7C%3A2%5E%7B2x%7D%3E0%5C%5C%5C%5C5%5Ccdot%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7B2x%7D-7%5Ccdot%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7Bx%7D%2B2%5Cgeq%200%5C%5C%5C%5Ct%3D%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7Bx%7D%3E0%5C%3B%20%5C%3B%20%2C%5C%3B%20%5C%3B%20%5C%3B%20%5C%3B%205t%5E2-7t%2B2%5Cgeq%200%5C%3B%20%5C%3B%20%2C%5C%3B%20%5C%3B%20D%3D49-40%3D9%5C%3B%20%2C%5C%3B%20%5C%3B%20t_%7B1%2C2%7D%3D%5Cfrac%7B7%5Cpm%203%7D%7B10%7D%5C%3B%20%2C%5C%5C%5C%5Ct_1%3D%5Cfrac%7B2%7D%7B5%7D%5C%3B%20%5C%3B%20%2C%5C%3B%20%5C%3B%20t_2%3D1%5C%5C%5C%5C5%28t-%5Cfrac%7B2%7D%7B5%7D%29%28t-1%29%5Cgeq%200%5C%3B%20%5C%3B%20%5C%3B%20%5C%3B%20%5C%3B%20%2B%2B%2B%5B%5C%2C%20%5Cfrac%7B2%7D%7B5%7D%5C%2C%20%5D---%5B%5C%2C%201%5C%2C%20%5D%2B%2B%2B%5C%5C%5C%5Ct%5Cleq%20%5Cfrac%7B2%7D%7B5%7D%5C%3B%20%5C%3B%20%5C%3B%20ili%5C%3B%20%5C%3B%20%5C%3B%20t%5Cgeq%201)
![a)\; \; (\frac{5}{2})^{x}\leq \frac{2}{5}\; \; \to \; \; (\frac{5}{2})^{x}\leq (\frac{5}{2})^{-1}\; \; ,\; \; x\leq -1\\\\b)\; \; (\frac{5}{2})^{x}\geq 1\; \; \to \; \; \; (\frac{5}{2})^{x}\geq (\frac{5}{2})^0\; \; \; ,\; \; \; x\geq 0\\\\Otvet:\; \; x\in (-\infty ,-1\, ]\cup [\, 0,+\infty )\; .](https://tex.z-dn.net/?f=a%29%5C%3B%20%5C%3B%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7Bx%7D%5Cleq%20%5Cfrac%7B2%7D%7B5%7D%5C%3B%20%5C%3B%20%5Cto%20%5C%3B%20%5C%3B%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7Bx%7D%5Cleq%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7B-1%7D%5C%3B%20%5C%3B%20%2C%5C%3B%20%5C%3B%20x%5Cleq%20-1%5C%5C%5C%5Cb%29%5C%3B%20%5C%3B%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7Bx%7D%5Cgeq%201%5C%3B%20%5C%3B%20%5Cto%20%5C%3B%20%5C%3B%20%5C%3B%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E%7Bx%7D%5Cgeq%20%28%5Cfrac%7B5%7D%7B2%7D%29%5E0%5C%3B%20%5C%3B%20%5C%3B%20%2C%5C%3B%20%5C%3B%20%5C%3B%20x%5Cgeq%200%5C%5C%5C%5COtvet%3A%5C%3B%20%5C%3B%20x%5Cin%20%28-%5Cinfty%20%2C-1%5C%2C%20%5D%5Ccup%20%5B%5C%2C%200%2C%2B%5Cinfty%20%29%5C%3B%20.)