1)Δ SBC
SB² = 12² + 20² = 544.
2)ΔABC
AB² = 16² - 12² = 112
3)ΔASB
AS² = 544 + 112 = 676, AS = √676= 26
4)|AS+SC+CB| = |26+20 +12| = 58
3. 2(7-x) = 10(x-4)-3(5-x)
14 - 2x = 10x - 40 - 15 + 3x
14 + 40 + 15 = 10x + 3x + 2x
15x = 69
x = 4.6
5. (6-4b)(2b+1) = 12b + 6 - 8b^2 - 4b = -8b^2 + 8b + 6
![\dispaystyle log_{11}(x+4)+log_{11}(x-7)=log_{11}(7-x)](https://tex.z-dn.net/?f=%5Cdispaystyle+log_%7B11%7D%28x%2B4%29%2Blog_%7B11%7D%28x-7%29%3Dlog_%7B11%7D%287-x%29)
найдем ОДЗ
![\dispaystyle \left \{ {{x+4\ \textgreater \ 0} \atop {x-7\ \textgreater \ 0; 7-x\ \textgreater \ 0}} \right.\\ \left \{ {{x\ \textgreater \ -4} \atop {x\ \textgreater \ 7; x\ \textless \ 7}} \right.](https://tex.z-dn.net/?f=%5Cdispaystyle++%5Cleft+%5C%7B+%7B%7Bx%2B4%5C+%5Ctextgreater+%5C+0%7D+%5Catop+%7Bx-7%5C+%5Ctextgreater+%5C+0%3B+7-x%5C+%5Ctextgreater+%5C+0%7D%7D+%5Cright.%5C%5C+%5Cleft+%5C%7B+%7B%7Bx%5C+%5Ctextgreater+%5C+-4%7D+%5Catop+%7Bx%5C+%5Ctextgreater+%5C+7%3B+x%5C+%5Ctextless+%5C+7%7D%7D+%5Cright.++)
Одновременно x>7 и x<7 быть не может. Значит решений нет