252 = 2*2*3*3*7 = 4*9*7 = 36*7 = 63*4 = 6*42 =21*12 = 9*28 = 36*7 = 126*2
Смотрим прикреплённый файл
Sec(65*6)=sec(390)=sec(30+360)=sec(30)=2√3/3
2)
![\frac{3x+1}{2} = \frac{2x-3}{5}](https://tex.z-dn.net/?f=+%5Cfrac%7B3x%2B1%7D%7B2%7D+%3D+%5Cfrac%7B2x-3%7D%7B5%7D+)
![\frac{3x+1}{2} - \frac{2x+3}{5} =0](https://tex.z-dn.net/?f=+%5Cfrac%7B3x%2B1%7D%7B2%7D+-+%5Cfrac%7B2x%2B3%7D%7B5%7D++%3D0)
первую дробь умножаем на 5. Вторую дробь на 2.
![\frac{15x+5}{10} - \frac{4x+6}{10}](https://tex.z-dn.net/?f=+%5Cfrac%7B15x%2B5%7D%7B10%7D+-+%5Cfrac%7B4x%2B6%7D%7B10%7D+)
![\frac{15x+5-4x+6}{10} =[tex] \frac{11x+11}{10}](https://tex.z-dn.net/?f=+%5Cfrac%7B15x%2B5-4x%2B6%7D%7B10%7D+%3D%5Btex%5D+%5Cfrac%7B11x%2B11%7D%7B10%7D+)
11x=1,1
x=0,1
3)
![\frac{x-3}{6} +x= \frac{2x-1}{3} - \frac{4-x}{2}](https://tex.z-dn.net/?f=+%5Cfrac%7Bx-3%7D%7B6%7D+%2Bx%3D+%5Cfrac%7B2x-1%7D%7B3%7D+-+%5Cfrac%7B4-x%7D%7B2%7D+)
![\frac{x-3}{6} +x- \frac{2x+1}{3} + \frac{4-x}{2}](https://tex.z-dn.net/?f=+%5Cfrac%7Bx-3%7D%7B6%7D+%2Bx-+%5Cfrac%7B2x%2B1%7D%7B3%7D+%2B+%5Cfrac%7B4-x%7D%7B2%7D+)
приводим к общему знаменателю
первую дробь не умножаем . х - умножаем на 6.вторую дробь умножаем на 2 . А третью дробь на 3 БУДЕТ :
![\frac{x-3}{6} - \frac{6x}{6} - \frac{4x-2}{6} + \frac{12-3x}{6}](https://tex.z-dn.net/?f=+%5Cfrac%7Bx-3%7D%7B6%7D+-+%5Cfrac%7B6x%7D%7B6%7D+-+%5Cfrac%7B4x-2%7D%7B6%7D+%2B+%5Cfrac%7B12-3x%7D%7B6%7D+)
![\frac{x-3+6x-4x+2+12-3x}{6}](https://tex.z-dn.net/?f=+%5Cfrac%7Bx-3%2B6x-4x%2B2%2B12-3x%7D%7B6%7D+)
=
![\frac{11}{6}](https://tex.z-dn.net/?f=+%5Cfrac%7B11%7D%7B6%7D+)
=
![1 \frac{5}{6}](https://tex.z-dn.net/?f=1+%5Cfrac%7B5%7D%7B6%7D+)
Ответ :
![1 \frac{5}{6}](https://tex.z-dn.net/?f=1+%5Cfrac%7B5%7D%7B6%7D+)
<span>-5х(х-0,4)-3(-1,2-0,5х)=
=-5x</span>²+2x+3.6+1.5x=
=-5x²+3.5x+3.6