4a^2-25b^2+36b^2-9f^2=9b^2-5a^2
- + - +
______.______o________.______
-1 1 2
![log_2x \leq \frac{2}{log_2x-1} \\ x\ \textgreater \ 0, \ log_2x-1 \neq 0\\ x\ \textgreater \ 0, x \neq 2\\ log_2x=a\\ a \leq \frac{2}{a-1} \\ \frac{a(a-1)-2}{a-1} \leq 0\\ \frac{a^2-a-2}{a-1} \leq 0\\ \frac{(a+1)(a-2)}{a-1} \leq 0\\ ...\\](https://tex.z-dn.net/?f=log_2x+%5Cleq++%5Cfrac%7B2%7D%7Blog_2x-1%7D+%5C%5C%0Ax%5C+%5Ctextgreater+%5C+0%2C+%5C+log_2x-1+%5Cneq+0%5C%5C%0Ax%5C+%5Ctextgreater+%5C+0%2C+x+%5Cneq+2%5C%5C%0Alog_2x%3Da%5C%5C%0Aa+%5Cleq++%5Cfrac%7B2%7D%7Ba-1%7D+%5C%5C%0A+%5Cfrac%7Ba%28a-1%29-2%7D%7Ba-1%7D++%5Cleq+0%5C%5C%0A+%5Cfrac%7Ba%5E2-a-2%7D%7Ba-1%7D++%5Cleq+0%5C%5C%0A+%5Cfrac%7B%28a%2B1%29%28a-2%29%7D%7Ba-1%7D++%5Cleq+0%5C%5C%0A...%5C%5C)
![log_2x \leq -1, \ 1\ \textless \ log_2x \leq 2\\ log_2x \leq log_20,5, \ log_22\ \textless \ log_2x\ \leq log_24\\ x \leq 0,5, \ 2\ \textless \ x\ \leq 4\\ Answer: \ x\in(0;0,5]U(2;4]](https://tex.z-dn.net/?f=log_2x+%5Cleq+-1%2C+%5C+1%5C+%5Ctextless+%5C+log_2x+%5Cleq+2%5C%5C%0Alog_2x+%5Cleq+log_20%2C5%2C+%5C+log_22%5C+%5Ctextless+%5C+log_2x%5C+%5Cleq+log_24%5C%5C%0Ax+%5Cleq+0%2C5%2C+%5C+2%5C+%5Ctextless+%5C+x%5C+%5Cleq%C2%A04%5C%5C%0AAnswer%3A+%5C+x%5Cin%280%3B0%2C5%5DU%282%3B4%5D)
480/a + 2 = 480/b
480 - (a+b)*3 = 60
Преобразуем к виду (выполним замену)
480-(480/((480/b)-2)+b)*3=60
b = 60 (км/ч)
a = 480 / (480 / b - 2) = 80 (км/ч)
Сначала раскрываешь скобки x2-9x+2x-18=0 Складываешь x и получаешь
X2-7x-18=0
D=49-4*(-18)=49+72=121
Корень из D=11
X1=7+11/2=9
X2=7-11/2=-2