học ngu tự mà lm đi hỏi con mẹ mày

Ta có : 1+3+5+7+9+...+x=100

   <=> (x+1).[(x-1):2+1]:2=100

                (x+1).[x-1/2+1]=200

                     (x+1).x+1/2=200

                      (x+1).(x+1)=400

                              (x+1)²=400

   => \(\orbr{\begin{cases}x+1=20\\x+1=-20\end{cases}}\)

Mà 1+3+5+7+9+...+x=100

Nên x+1=20

  =>      x=19

ko ghi đề

\(=25,97+\left(6,54+103,46\right)\)

\(=25,97+110\)

\(=135,97\)

a/135,97

b/1500

c/10

c) \(\dfrac{x+4}{20}=\dfrac{5}{x+4}\)

⇔\(\left(x+4\right)\left(x+4\right)=100\)

⇔\(\left(x+4\right)^2=10^2\)

⇔\(\left[{}\begin{matrix}x+4=10\\x+4=-10\end{matrix}\right.\)

⇔\(\left[{}\begin{matrix}x=6\\x=-14\end{matrix}\right.\)

\(c,ĐK:x\ne-4\\ PT\Leftrightarrow\left(x+4\right)^2=100\\ \Leftrightarrow\left[{}\begin{matrix}x+4=10\\x+4=-10\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\left(tm\right)\\x=-14\left(tm\right)\end{matrix}\right.\\ d,ĐK:x\ne-2;x\ne-3\\ PT\Leftrightarrow\left(x-1\right)\left(x+3\right)=\left(x-2\right)\left(x+2\right)\\ \Leftrightarrow x^2+2x-3=x^2-4\\ \Leftrightarrow2x=-1\Leftrightarrow x=-\dfrac{1}{2}\left(tm\right)\)

\(A=\dfrac{1}{2}\left(x-3\right)^2+10\ge10\\ A_{min}=10\Leftrightarrow x-3=0\Leftrightarrow x=3\)

\(A=\dfrac{1}{2}\left(x-3\right)^2+10\ge10\forall x\)

Dấu '=' xảy ra khi x=3

Lê Phúc Đạt:

(x + 1) + (x + 2) +...+ (x + 100) = 5750

Đặt: (x + 1) + (x + 2) +...+ (x + 100) = S

Từ 1 đến 100 có 100 số hạng:

=> S = 100x + (1 + 2 +...+100)

     S = 100x + (100 + 1). 100 : 2

     S = 100x + 5050

=> 100x + 5050 = 5750

      100x             = 5750 - 5050

      100x             = 700

            x              = 700 : 100

            x              = 7

Vậy x = 7

Tham khảo nha!

ta có: (x+1)+(x+2)+(x+3)+....+(x+100)=5750

        =(x + x+ x+....+ x)+(1+2+3+....+100)=5750

    suy ra có 100x và 100 so hang

      =100x + 5050=5750

=100x=5750-5050

=100x=700

=x=700 : 100

=x=7

c) \(2x=3y=5z\)⇒\(\dfrac{x}{15}=\dfrac{y}{10}=\dfrac{z}{6}\)

Áp dụng tính chát dãy tỉ số bằng nhau, ta có:

\(\dfrac{x}{15}=\dfrac{y}{10}=\dfrac{z}{6}=\dfrac{x+y-z}{15+10-6}=\dfrac{95}{19}=5\)

⇒\(\left\{{}\begin{matrix}x=5.15=75\\y=5.10=50\\z=5.6=30\end{matrix}\right.\)

a) \(\dfrac{x-3}{x+5}=\dfrac{5}{7}\)

⇔\(7\left(x-3\right)=5\left(x+5\right)\)

⇔\(7x-21=5x+25\)

⇔\(7x-21-5x-25=0\)

⇔\(2x-46=0\)

⇔\(2x=46\)

⇔\(x=23\)

giúp mik phần b nha đc ko ???

a) \(x-270:45=120\)

\(x-270=120.45\)

\(x-270=5400\)

\(x=5400+270\)

\(x=5670\)

_____

b) \(575-\left(6\times x+70\right)=445\)

\(6\times x+70=575-445\)

\(6\times x+70=130\)

\(6\times x=130-70\)

\(6\times x=60\)

\(x=60:6\)

\(x=10\)

_____

c) \(x-105:21=15\)

\(x-105=15.21\)

\(x-105=315\)

\(x=315+105\)

\(x=420\)

_____

d) \(3200:\left(405-x\right)=8\)

\(405-x=3200:8\)

\(405-x=400\)

\(x=405-400\)

\(x=5\)

_____

i) \(43575-75\times x=42450\)

\(75.x=43575-42450\)

\(75.x=1125\)

\(x=1125:75\)

\(x=15\)

_____

e) \(8,75\times x+1,25\times x=20\)

\(x\times\left(8,75+1,25\right)=20\)

\(x\times10=20\)

\(x=20:10\)

\(x=2\)

ko cần giải câu b đâu