x.2+x.3+x.4+x=2130

x.(2+3+4+1)=2130

x.10=2130

x=2130:10

x=213

`x xx 2 + x xx3+x xx4+x=2130`

`x xx(2+3+4+1)=2130`

`x xx 10=2130`

`x=2130:10=213`

B

Chọn B

3A=1+1/3+...+1/3^99

=>2A=1-1/3^100=(3^100-1)/3^100

=>A=(3^100-1)/(2*3^100)

Ta có : X + X + X + X x 4 = 105 

            (X + X + X ) + 4X = 105 

           3X + 4X = 105 

            X x (3 + 4 ) = 105

            7x X = 105 

           X = 105 : 7

         X = 15

x+x+x+x*4=105

x.(1+1+1+4)=105

x.7=105

x=105:7

x=15

Vậy x=15

=Xx3+Xx4=105

Xx(3+4)=105

Xx7=105

X=105:7

X=LAM NOT

a) \(x\times4+\frac{1}{2}\times x=55,35\)

   \(x\times\left(4+\frac{1}{2}\right)=55,35\)

   \(x\times4,5=55,35\)

   \(x=55,35:4,5=12,3\)

b) \(x-20\%\times x=216\)

    \(x-0,2\times x=216\)

    \(x\times\left(1-0,2\right)=216\)

    \(x\times0,8=216\)

    \(x=216:0,8=270\)

Cảm ơn bn rất rất rất nhiều nha!!!😁😁😁

\(x^4+x^3-27x-27=0\)

\(\Leftrightarrow x^3\left(x+1\right)-27\left(x+1\right)=0\)

\(\Leftrightarrow\left(x+1\right)\left(x^3-27\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\x^3=3^3\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=3\end{matrix}\right.\)

120-(Xx3+Xx4)=50

    Xx3+Xx4      =120-50

Xx(3+4)            =70

Xx7                  =70

X                      =70:7

X                      =10

a: =>x^3(x-2)+10x(x-2)=0

=>(x-2)(x^3+10x)=0

=>x(x-2)(x^2+10)=0

=>x(x-2)=0

=>x=0 hoặc x=2

b: =>x^2*(x-3)-16(x-3)=0

=>(x-3)(x^2-16)=0

=>(x-3)(x+4)(x-4)=0

=>\(x\in\left\{3;4;-4\right\}\)

-x-6=-10

-x=(-10)+6

-x=-4

x=4

7-x=-5

x=7-(-5)

x=2

-x-6=-10

-x   =-10+6

-x   =4

x    =-4

7-x=-5

-x  =-5-7

-x  =-12

x   =12