20 + 20 + x = 60
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\(\dfrac{60}{x}-\dfrac{60}{x+20}=\dfrac{1}{2}\left(đk:x>0\right)\)
\(\Leftrightarrow\dfrac{120\left(x+20\right)-120x-x\left(x+20\right)}{2x\left(x+20\right)}=0\)
\(\Leftrightarrow120x+2400-120x-x^2-20x=0\)
\(\Leftrightarrow-x^2-20x+2400=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x_1=40\left(n\right)\\x_2=-60\left(l\right)\end{matrix}\right.\)
Vậy \(S=\left\{40\right\}\)
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Kết bạn nhé !
x + 10 = 20
x = 20 - 10
x = 10
x - 20 = 30
x = 30 + 20
x = 50
x . 20 = 40
x = 40 : 20
x = 2
x : 30 = 60
x = 60 x 30
x = 180
X + 10 = 20
X = 20 - 10=10
X . 20 = 40
40 : 20 = 2
X : 30 = 60
X = 60 . 30 = 1800
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{60}{x}-\dfrac{60}{x+2}=\dfrac{1}{20}\left(đk:x\ne0,x\ne-2\right)\)
\(\Leftrightarrow\dfrac{60x+120-60x}{x\left(x+2\right)}=\dfrac{1}{20}\)
\(\Leftrightarrow\dfrac{120}{x^2+2x}=\dfrac{1}{20}\Leftrightarrow x^2+2x=2400\)
\(\Leftrightarrow\left(x+1\right)^2=2401\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=49\\x+1=-49\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=48\\x=-50\end{matrix}\right.\)(thỏa đk)
Ta có: \(\dfrac{60}{x}-\dfrac{60}{x+2}=\dfrac{1}{20}\)
\(\Leftrightarrow x\left(x+2\right)=1200x+2400-1200x\)
\(\Leftrightarrow x^2+2x-2400=0\)
\(\Delta=2^2-4\cdot1\cdot\left(-2400\right)=9604\)
Vì \(\Delta>0\) nên phương trình có hai nghiệm phân biệt là:
\(\left\{{}\begin{matrix}x_1=\dfrac{-2-98}{2}=-50\left(nhận\right)\\x_2=\dfrac{-2+98}{2}=48\left(nhận\right)\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài làm
( 10 + 20 + 30 + ..... + 900 ) x ( 60 x 1 - 60 )
= ( 10 + 20 + 30 + ...... + 900 ) x ( 60 - 60 )
= ( 10 + 20 + 30 + ...... + 900 ) x 0
= 0
![](https://rs.olm.vn/images/avt/0.png?1311)
20 + 10 + 10 = 40 60 - 10 - 20 = 30
30 + 10 + 20 = 60 60 - 20 -10 = 30
30 + 20 + 10 = 60 70 + 10 - 20 = 60
20 + 10 + 10 =40 60 - 10 - 20 =30
30 + 10 + 20 =60 60 - 20 -10 =30
30 + 20 + 10 =60 70 + 10 - 20 =60
Số cần tìm:
60 - 20 - 20 = 20
Đáp số: 20
k mik nha
x=60-(20+20)
x=20