1)16000:100*15=2400 руб это 15%
2)16000-2400=13600 руб в феврале
2x-30+3x=5x-30
при х=1 то 5х-30=5-30=-25
х=0 то 5х-30=0-30=-30
х=-8 то 5х-30=-40-30=-70
5х-6+3х=8х-6
при х=1 то 8х-6=8-6=2
х=0 то 8х-6=0-6=-6
х=-8 то 8х-6=-64-6=-70
5(x-3)(x+3)
3(x-5a)(x+5a)
2a(a-y)(a+y)
a(x-2)(x+2)
x²-9b²-x³-8b³
(2x-5-7x+1)(2x-5+7x-1)=(-5x-4)(9x-6)=-3(5x+4)(3x-2)
b²-9+4b²+12b+9=5b²+12b
3x²-30x+75+10x-8x²=-5x²-20x+75
4) 3,(7)
Пусть x = 3,77 ... , тогда 10x = 37,77 ...
10x - x = 37,77 ... - 3,77 ...
9x = 34
![x= \frac{34}{9} =3 \frac{7}{9} \\\\3,(7)=3 \frac{7}{9}](https://tex.z-dn.net/?f=x%3D+%5Cfrac%7B34%7D%7B9%7D+%3D3+%5Cfrac%7B7%7D%7B9%7D+%5C%5C%5C%5C3%2C%287%29%3D3+%5Cfrac%7B7%7D%7B9%7D+)
β - угол четвёртой четверти значит Cosβ > 0
![Cos \beta = \sqrt{1-Sin ^{2} \beta } = \sqrt{1-(- \frac{12}{13}) ^{2} }= \sqrt{1- \frac{144}{169} }= \sqrt{ \frac{25}{169} }= \frac{5}{13}\\\\tg \beta = \frac{Sin \beta }{Cos \beta } = \frac{- \frac{12}{13} }{ \frac{5}{13} } =- \frac{12}{5}=-2,4 \\\\tg2 \beta = \frac{2tg \beta }{1-tg ^{2} \beta }=](https://tex.z-dn.net/?f=Cos+%5Cbeta+%3D+%5Csqrt%7B1-Sin+%5E%7B2%7D+%5Cbeta++%7D+%3D+%5Csqrt%7B1-%28-+%5Cfrac%7B12%7D%7B13%7D%29+%5E%7B2%7D++%7D%3D+%5Csqrt%7B1-+%5Cfrac%7B144%7D%7B169%7D+%7D%3D+%5Csqrt%7B+%5Cfrac%7B25%7D%7B169%7D+%7D%3D+%5Cfrac%7B5%7D%7B13%7D%5C%5C%5C%5Ctg+%5Cbeta+%3D+%5Cfrac%7BSin+%5Cbeta+%7D%7BCos+%5Cbeta+%7D+%3D+%5Cfrac%7B-+%5Cfrac%7B12%7D%7B13%7D+%7D%7B+%5Cfrac%7B5%7D%7B13%7D+%7D+%3D-+%5Cfrac%7B12%7D%7B5%7D%3D-2%2C4+%5C%5C%5C%5Ctg2+%5Cbeta+%3D+%5Cfrac%7B2tg+%5Cbeta+%7D%7B1-tg+%5E%7B2%7D+%5Cbeta++%7D%3D+++)
![= \frac{2*(-2,4)}{1-(-2,4) ^{2} }= \frac{-4,8}{1-5,76}= \frac{-4,8}{-4,76}= \frac{120}{119}=1 \frac{1}{119}](https://tex.z-dn.net/?f=%3D+%5Cfrac%7B2%2A%28-2%2C4%29%7D%7B1-%28-2%2C4%29+%5E%7B2%7D+%7D%3D+%5Cfrac%7B-4%2C8%7D%7B1-5%2C76%7D%3D+%5Cfrac%7B-4%2C8%7D%7B-4%2C76%7D%3D+%5Cfrac%7B120%7D%7B119%7D%3D1+%5Cfrac%7B1%7D%7B119%7D++++)