<span>0,2x-0.4=0,5x-2.5
2.5 -0.4 = 0.5x-0.2x
2.1 = 0.3x
x =2.1/0.3 = 21/3 =7
x=7
</span><span>
</span>
1,28
0,8*0,8=0.64
0.64/0.5=1.28
Вроде как 1) (2x+a)(a-b) 2) (3-b)(x+y)
A²+3a/9-a²= a(a-3)/(3-a)(3-a)= -a(3-a)/(3-a)(3-a)=a/3-a (/-знак дроби)
√3х²-5х=√х²+2х-5
√9х²-5х=√х²+2х-5
3х-5х=х+2х-5
3х-5х-х-2х=-5
-5х=-5
Х=1