2cos315=2cos(270+45)=2sin45=2*(√2/2)=√2
sin210=sin(180+30)=-sin30=-√3/2
tg420=tg(360+60)=tg60=√3
2cos315+sin210+tg420=√2-√3/2+√3
Найдем, какие значение принимает 7а:
![\displaystyle \frac{7}5\ \textless \ a\ \textless \ 3.5\\\\\frac{7*7}5\ \textless \ 7a\ \textless \ \frac{7*7}2\\\\\frac{49}5\ \textless \ 7a\ \textless \ \frac{49}2](https://tex.z-dn.net/?f=%5Cdisplaystyle+%5Cfrac%7B7%7D5%5C+%5Ctextless+%5C++a%5C+%5Ctextless+%5C++3.5%5C%5C%5C%5C%5Cfrac%7B7%2A7%7D5%5C+%5Ctextless+%5C+7a%5C+%5Ctextless+%5C+%5Cfrac%7B7%2A7%7D2%5C%5C%5C%5C%5Cfrac%7B49%7D5%5C+%5Ctextless+%5C+7a%5C+%5Ctextless+%5C+%5Cfrac%7B49%7D2)
Значения, которые принимает 2b:
![\displaystyle -2,5\ \textless \ b \ \textless \ - \frac{1}3\\\\-\frac{5*2}2\ \textless \ 2b\ \textless \ -\frac{2}3\\\\-5\ \textless \ 2b\ \textless \ -\frac{2}3](https://tex.z-dn.net/?f=%5Cdisplaystyle+-2%2C5%5C+%5Ctextless+%5C++b+%5C+%5Ctextless+%5C++-+%5Cfrac%7B1%7D3%5C%5C%5C%5C-%5Cfrac%7B5%2A2%7D2%5C+%5Ctextless+%5C+2b%5C+%5Ctextless+%5C+-%5Cfrac%7B2%7D3%5C%5C%5C%5C-5%5C+%5Ctextless+%5C+2b%5C+%5Ctextless+%5C+-%5Cfrac%7B2%7D3)
А теперь 7a-2b:
![\displaystyle \frac{49}5-(-5)\ \textless \ 7a-2b\ \textless \ \frac{49}2-\bigg(-\frac{2}3\bigg)\\\\\\\frac{49}5+\frac{5*5}5\ \textless \ 7a-2b\ \textless \ \frac{49*3}{6}+\frac{2*2}{6}\\\\\\\frac{74}{5}\ \textless \ 7a-2b\ \textless \ \frac{151}{6}\\\\\\14.8\ \textless \ 7a-2b\ \textless \ 25.1(6)\\\\\\15,\,\,\,16,\,\,\,17,\,\,\,18,\,\,\,19,\,\,\,20,\,\,\,21,\,\,\,22,\,\,\,23,\,\,\,24,\,\,\,25\\\\\\\text{OTBET}:\,\,11](https://tex.z-dn.net/?f=%5Cdisplaystyle+%5Cfrac%7B49%7D5-%28-5%29%5C+%5Ctextless+%5C+7a-2b%5C+%5Ctextless+%5C+%5Cfrac%7B49%7D2-%5Cbigg%28-%5Cfrac%7B2%7D3%5Cbigg%29%5C%5C%5C%5C%5C%5C%5Cfrac%7B49%7D5%2B%5Cfrac%7B5%2A5%7D5%5C+%5Ctextless+%5C+7a-2b%5C+%5Ctextless+%5C+%5Cfrac%7B49%2A3%7D%7B6%7D%2B%5Cfrac%7B2%2A2%7D%7B6%7D%5C%5C%5C%5C%5C%5C%5Cfrac%7B74%7D%7B5%7D%5C+%5Ctextless+%5C+7a-2b%5C+%5Ctextless+%5C+%5Cfrac%7B151%7D%7B6%7D%5C%5C%5C%5C%5C%5C14.8%5C+%5Ctextless+%5C+7a-2b%5C+%5Ctextless+%5C+25.1%286%29%5C%5C%5C%5C%5C%5C15%2C%5C%2C%5C%2C%5C%2C16%2C%5C%2C%5C%2C%5C%2C17%2C%5C%2C%5C%2C%5C%2C18%2C%5C%2C%5C%2C%5C%2C19%2C%5C%2C%5C%2C%5C%2C20%2C%5C%2C%5C%2C%5C%2C21%2C%5C%2C%5C%2C%5C%2C22%2C%5C%2C%5C%2C%5C%2C23%2C%5C%2C%5C%2C%5C%2C24%2C%5C%2C%5C%2C%5C%2C25%5C%5C%5C%5C%5C%5C%5Ctext%7BOTBET%7D%3A%5C%2C%5C%2C11)
Y=(-4x+7)/3= -4x/3+7/3
(1;1) , (7;-7)-искомые точки,
график пересекает ось OX в (7/4; 0) , ось OY в точке (0; 7/3)