Số số hạng của dãy là : \(\left(45-1\right)\div4+1=12\)( số )

Ta có :

\(\left(x+1\right)+\left(x+5\right)+\left(x+9\right)+....+\left(x+45\right)=331,2\)

\(\Leftrightarrow12\times x+\frac{\left(45+1\right)\times12}{2}=331,2\)

\(\Leftrightarrow12\times x+276=331,2\)

\(\Leftrightarrow12\times z=55,2\)

\(\Leftrightarrow x=4,6\)

Vậy \(x=4,6\)

Câu 1:

\(3x\left(12x+4\right)+9x\left(4x+3\right)\)

\(\Leftrightarrow3x\left(12x+4\right)+3x\left[3.\left(4x+3\right)\right]\)

\(\Leftrightarrow3x\left(12x+4\right)+3x\left(12x+6\right)\)

\(\Leftrightarrow3x\left[12x+4+12x+6\right]\)

\(\Leftrightarrow3x.\left(24x+10\right)\)

\(\Leftrightarrow72x^2+30x\)

Câu 2:

\(x\left(5+2x\right)+2x^2\left(x-1\right)\)

\(\Leftrightarrow5x+2x^2+2x^3-2x^2\)

\(\Leftrightarrow2x^3+5x\)

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|x-2,2| =|0,2-x|<=> |x-2,2| -|0,2-x| = 0

|x-2,2|>=0

|0,2-x|>=0

mà |x-2,2|-|0,2-x| =0            

hoặc  =>x-2,2=0=> x =2

hoặc  =>0,2-x=0=> x =0,2

x . 15 + x + 15 = 463

x . 15 + x = 463 - 15

x . 15 + x = 448

x . ( 15 + 1 ) = 448

x . 16 = 448

x = 448 : 16

x = 28

\(\left(2x-3\right)\left(x+3\right)\left(5-x\right)\)

\(=\left(2x^2+6x-3x-9\right)\left(5-x\right)\)

\(=10x^2+30x-15x-45-2x^3-6x^2+3x^2+9x\)

\(=-2x^3+7x^2+24x-45\)

Ta có: -12.(x-5)+7(3-x)=-12x-(-60)+21-7x=-12x-7x+81=-19x+81=5 => -19x=76

=> x=-4

Vậy x=-4

20 000 - x * 5 =12485
x*5=20 000 - 12485
x*5=7515
x=7515:5
x=1503

cảm ơn bn nha

x x 10 -x = 1

x x 9 = 1

x =1:9

x =1/9

1/9 là một phần chín nhé

thank you nha!!!