AB=2.7;AC=3.2;
3.2-2.7=0.5
BC=0.5
ОТВЕТ 0.5
<span>100a^2-9a^2x^2=ещкере фейс
</span>
1)cosa*cos3a-sina*sin3a =cos(a+3a)=cos4a
2) sin2a*cosa+cos2a*sina = sin(2a+a)=sin3a
3) sin40*cos5+cos40*sin5 =sin(40+5)=sin45=√2/2
4) (tg7П/15-tg2П/15)/1+tg7П/15*tg2П/15=tg(7П/15-2П/15)=tg(п/3)=√3
5) sina=-4/5;П<a<3П/2; cosa-?
cosa на отрезке П<a<3П/2 отрицателен.
1-sin^2a=cos^2a=1-16/25=9/25
cosa=-3/5
Вся книга - 1
1-2/5=3/5 =0,6 книги - остаток после первого дня
60%=0,6
0,6*0,6=0,36 книги - прочитал во второй день
0,4+0,36=0,76 книги - за два дня
1-0,76=0,24 книги - в третий день
0,36-0,24=0,12 книги - разница между вторым и третьим днями
30:0,12=250 страниц - вся книга
![\displaystyle \frac{3}{cos^2(x- \frac{17 \pi }{2})}+ \frac{4}{sinx}-4=0\\\\ \frac{3}{cos^2(8 \pi + \frac{ \pi }{2}-x)}+ \frac{4}{sinx}-4=0\\\\ \frac{3}{sin^2x}+ \frac{4}{sinx}-4=0\\\\\ \frac{1}{sinx}=t\\\\3t^2+4t-4=0\\\\D=16+48=64=8^2\\\\t_{1.2}= \frac{-4\pm 8}{6}\\\\t_1=-2; t_2=2/3](https://tex.z-dn.net/?f=%5Cdisplaystyle++%5Cfrac%7B3%7D%7Bcos%5E2%28x-+%5Cfrac%7B17+%5Cpi+%7D%7B2%7D%29%7D%2B+%5Cfrac%7B4%7D%7Bsinx%7D-4%3D0%5C%5C%5C%5C+%5Cfrac%7B3%7D%7Bcos%5E2%288+%5Cpi+%2B+%5Cfrac%7B+%5Cpi+%7D%7B2%7D-x%29%7D%2B+%5Cfrac%7B4%7D%7Bsinx%7D-4%3D0%5C%5C%5C%5C+%5Cfrac%7B3%7D%7Bsin%5E2x%7D%2B+%5Cfrac%7B4%7D%7Bsinx%7D-4%3D0%5C%5C%5C%5C%5C+%5Cfrac%7B1%7D%7Bsinx%7D%3Dt%5C%5C%5C%5C3t%5E2%2B4t-4%3D0%5C%5C%5C%5CD%3D16%2B48%3D64%3D8%5E2%5C%5C%5C%5Ct_%7B1.2%7D%3D+%5Cfrac%7B-4%5Cpm+8%7D%7B6%7D%5C%5C%5C%5Ct_1%3D-2%3B+t_2%3D2%2F3++++++++)
![\displaystyle \frac{1}{sinx}=-2; sin x=- \frac{1}{2}\\\\ \frac{1}{sinx}= \frac{2}{3}; sinx= \frac{3}{2}](https://tex.z-dn.net/?f=%5Cdisplaystyle++%5Cfrac%7B1%7D%7Bsinx%7D%3D-2%3B+sin+x%3D-+%5Cfrac%7B1%7D%7B2%7D%5C%5C%5C%5C+%5Cfrac%7B1%7D%7Bsinx%7D%3D+%5Cfrac%7B2%7D%7B3%7D%3B+sinx%3D+%5Cfrac%7B3%7D%7B2%7D+++++)
во втором случае нет корней
![\displaystyle sinx=- \frac{1}{2}\\\\x=(-1)^n *arcsin(- \frac{1}{2})+ \pi n; n\in Z\\\\x_1=- \frac{ \pi }{6}+2 \pi n; n\in Z\\\\x_2=- \frac{5 \pi }{6}+2 \pi n; n\in Z](https://tex.z-dn.net/?f=%5Cdisplaystyle+sinx%3D-+%5Cfrac%7B1%7D%7B2%7D%5C%5C%5C%5Cx%3D%28-1%29%5En+%2Aarcsin%28-+%5Cfrac%7B1%7D%7B2%7D%29%2B+%5Cpi+n%3B+n%5Cin+Z%5C%5C%5C%5Cx_1%3D-+%5Cfrac%7B+%5Cpi+%7D%7B6%7D%2B2+%5Cpi+n%3B+n%5Cin+Z%5C%5C%5C%5Cx_2%3D-+%5Cfrac%7B5+%5Cpi+%7D%7B6%7D%2B2+%5Cpi+n%3B+n%5Cin+Z+++)
выбор корней на промежутке
![\displaystyle [- \frac{7 \pi }{2};-2 \pi ]](https://tex.z-dn.net/?f=%5Cdisplaystyle+%5B-+%5Cfrac%7B7+%5Cpi+%7D%7B2%7D%3B-2+%5Cpi+%5D+)
промежуток находится на втором обороте в отрицательную сторону
значит
![\displaystyle x_1=- \frac{ \pi }{6}-2 \pi =- \frac{13 \pi }{6}\\\\\ x_2=- \frac{5 \pi }{6}-2 \pi =- \frac{17 \pi }{6}](https://tex.z-dn.net/?f=%5Cdisplaystyle+x_1%3D-+%5Cfrac%7B+%5Cpi+%7D%7B6%7D-2+%5Cpi+%3D-+%5Cfrac%7B13+%5Cpi+%7D%7B6%7D%5C%5C%5C%5C%5C+x_2%3D-+%5Cfrac%7B5+%5Cpi+%7D%7B6%7D-2+%5Cpi+%3D-+%5Cfrac%7B17+%5Cpi+%7D%7B6%7D++++)