\(1+2+3+4+...+x=465\)

\(\Rightarrow x.\left(x+1\right):2=465\)

\(\Rightarrow x.\left(x+1\right)=465.2\)

\(\Rightarrow x.\left(x+1\right)=930\)

\(\Rightarrow x.\left(x+1\right)=30.31\)

\(\Rightarrow x=30\)

x=30 

tick minh nhaaaaaaaaaaa

 1 + 2 + 3 + .... + x = x( x + 1 )/2 = 465 ⇔ x² + n = 930 ⇔ x² + x - 930 = 0 ⇔ x = 30 hoặc x = -31 ( loại ) vì x > 3 căn cứ theo đề bài. Vậy x = 30 

30

tick đúng nhaaa

a) 

151 - 2 x ( x-6 ) = 2227 : 17

        2 x ( x-6 ) =   131

        2 x ( x-6 ) =  151 - 131

        2 x ( x-6 ) =    20

               x-6   = 20 : 2

               x - 6 =   10

               x     = 10 + 6

              x      =   16 

b) $\frac{\mathrm{\backslash (\backslash dfrac\{1\}\{3\}\backslash )\; x\; X\; =}}{}$

\(\dfrac{2}{3}-\dfrac{1}{4}=\dfrac{5}{12}\\ X=\dfrac{5}{12}:\dfrac{1}{3}=\dfrac{5}{4}\)

a, 151 - 2 x ( x-6 ) = 2227 : 17

    2 x ( x-6 ) =   131

    2 x ( x-6 ) =  151 - 131

    2 x ( x-6 ) =    20

    x-6   = 20 : 2

    x - 6 =   10

    x = 10 + 6

    x =  16 

 1+2+3+4+5+...+x=465

\(\frac{x.\left(x+1\right)}{2}=465\)

x.(x+1)=465.2

x(x+1)=930

x.(x+1)=30.31

x=30

x=30                          **** di minh giai ro rang cho

Bạn Minh Huyền sao Lại viết

\(\frac{x.\left(x+1\right)}{2}=465\)

Mình\(không\)hiểu

3( x - 5 )( x - 2 )( x + 2 ) + 4 = 7 + 3x³ - 15x²

<=> ( 3x - 15 )( x² - 4 ) + 4 - 7 = 3x³ - 15x²

<=> 3x³ - 12x - 15x² + 60 - 3 = 3x³ - 15x²

<=> 57 = 3x³ - 15x² - 3x³ + 12x + 15x²

<=> 57 = 12x

<=> x = 57/12 = 19/4

Tìm x biết:

3(x - 5)(x - 2)(x + 2) + 4 = 7 + 3x³ - 15x²

\(3\left(x-5\right)\left(x-2\right)\left(x+2\right)+4=3x^3-15x^2-12x=64\)

\(7+3^3+\left(-15\right)x^2=3x^3-15x^2+7\)

\(3x^3-15x^2-12x+64=3x^3-15x^2+7\)

\(\Rightarrow\frac{19}{4}\)

\(3\left(x-5\right)\left(x-2\right)\left(x+2\right)+4=7+3x^3-15x^2\)

\(\Leftrightarrow3\left(x-5\right)\left(x^2-4\right)+4=7+3x^3-15x^2\)

\(\Leftrightarrow3\left(x^3-4x-5x^2+20\right)+4=7+3x^3-15x^2\)

\(\Leftrightarrow3x^3-12x-15x^2+60+4=7+3x^3-15x^2\)

\(\Leftrightarrow-12x+64=7\Leftrightarrow-12x=-57\Leftrightarrow x=\frac{19}{4}\)

\(1+2+3+...+x=465\)

\(\Rightarrow\frac{x\left(x+1\right)}{2}=465\)

\(\Rightarrow x\left(x+1\right)=930\)

\(\Rightarrow x\left(x+1\right)=30.31\)

=> x = 30

Vậy x = 30

1 + 2 + 3 + .... + n = n( n + 1 )/2 = 465 ⇔ n² + n = 930

⇔ n² + n - 930 = 0 ⇔ n = 30 hoặc n = -31 ( loại ) vì n > 3 căn cứ theo đề bài.

Vậy n = 30

1+2+3+...+x = 465

=> \(\frac{x\left(x+1\right)}{2}\) = 465

=> x(x+1) = 930

=> x(x+1) = 30.31

=> x = 30

a.     x +\(\frac{1}{5}=\frac{-4}{9}\)
=>    x          = \(\frac{-4}{9}-\frac{1}{5}\)
=>    x          = \(\frac{-29}{45}\)
b.    2-(x+\(\frac{3}{7}\))= \(\frac{9}{-21}\)
=>  2-x -\(\frac{3}{7}\)= \(\frac{9}{-21}\)
=> -x+\(\frac{11}{7}\)= \(\frac{9}{-21}\)
=> x               = 2

Câu c tương tự câu b cứ làm từ từ là ra.
Chọn đúng cho mình nha các bạn

a) \(x^3+15x^2+75x=-125\)

\(\Leftrightarrow x^3+15x^2+75x+125=0\)

\(\Leftrightarrow x^3+125+15x^2+75x=0\)

\(\Leftrightarrow\left(x+5\right)\left(x^2+5x+25\right)+15x\left(x+5\right)=0\)

\(\Leftrightarrow\left(x+5\right)\left(x^2+20x+25\right)=0\)

\(TH1:x+5=0\Leftrightarrow x=-5\)

\(TH2:x^2+20x+25=0\)

\(\Leftrightarrow\left(x+10\right)^2=75\)

\(\Leftrightarrow\orbr{\begin{cases}x=\sqrt{75}-10\\x=-\sqrt{75}-10\end{cases}}\)

b) \(x\left(x-3\right)\left(x+3\right)-\left(x+2\right)\left(x^2-2x+4\right)=10\)

\(\Leftrightarrow x\left(x^2-9\right)-\left(x^3+8\right)=10\)

\(\Leftrightarrow x^3-9x-x^3-8=9\)

\(\Leftrightarrow-9x=17\)

\(\Leftrightarrow x=\frac{-17}{9}\)