Пусть x(см) - шир. , тогда: (х+8)(см) - длин.
По условию: 2х+2(х+8)=20
2х+2х+16=20
4х=4
х=1
1(см) - шир.
1+8=9(см) - длин.
S = 9•1 = 9(см)
!!!!!!!!!!!!!!!!!!!!!!!!!!!!
X^2+4x+8x-x-x^2+x-4+1=0
12x-3=0
12x=3
x=0,25
![tg(4x+\frac{\pi}{3})<2\\\\-\frac{\pi}{2}+\pi n<4x+\frac{\pi}{3}<arctg2+\pi n](https://tex.z-dn.net/?f=tg%284x%2B%5Cfrac%7B%5Cpi%7D%7B3%7D%29%3C2%5C%5C%5C%5C-%5Cfrac%7B%5Cpi%7D%7B2%7D%2B%5Cpi+n%3C4x%2B%5Cfrac%7B%5Cpi%7D%7B3%7D%3Carctg2%2B%5Cpi%C2%A0n)
Вычтем из всех частей неравенства число
![\frac{\pi}{3}](https://tex.z-dn.net/?f=%5Cfrac%7B%5Cpi%7D%7B3%7D)
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![-\frac{5\pi}{6}+\pi n<4x<-\frac{\pi}{3}+arctg2+\pi n\; |:4\\\\-\frac{5\pi}{24}+\frac{\pi n}{4}<x<-\frac{\pi}{12}+\frac{1}{4}arctg2+\frac{\pi n}{4},n\in Z](https://tex.z-dn.net/?f=-%5Cfrac%7B5%5Cpi%7D%7B6%7D%2B%5Cpi+n%3C4x%3C-%5Cfrac%7B%5Cpi%7D%7B3%7D%2Barctg2%2B%5Cpi+n%5C%3B+%7C%3A4%5C%5C%5C%5C-%5Cfrac%7B5%5Cpi%7D%7B24%7D%2B%5Cfrac%7B%5Cpi+n%7D%7B4%7D%3Cx%3C-%5Cfrac%7B%5Cpi%7D%7B12%7D%2B%5Cfrac%7B1%7D%7B4%7Darctg2%2B%5Cfrac%7B%5Cpi+n%7D%7B4%7D%2Cn%5Cin+Z)