tìm x biết (x+1)+(x+3)+(x+5)+(x+7)+(x+9)=750
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\(x-\frac{3}{5}=\frac{4}{7}\) \(x+\frac{3}{5}=\frac{4}{3}\) \(-x-\frac{2}{7}=-\frac{8}{9}\)
\(x=\frac{4}{7}+\frac{3}{5}\) \(x=\frac{4}{3}-\frac{3}{5}\) \(-x=-\frac{8}{9}+\frac{2}{7}\)
\(x=\frac{41}{35}\) \(x=\frac{11}{15}\) \(-x=-\frac{38}{63}\)
\(x=\frac{38}{63}\)
\(\frac{7}{9}-x=\frac{1}{5}\)
\(x=\frac{7}{9}-\frac{1}{5}\)
\(x=\frac{26}{45}\)
Bài 1:
a) \(x.\dfrac{3}{4}=\dfrac{9}{14}\)
\(\Rightarrow x=\dfrac{9}{14}:\dfrac{3}{4}\)
\(\Rightarrow x=\dfrac{6}{7}\)
b) \(x:\dfrac{5}{9}=\dfrac{3}{10}\)
\(\Rightarrow x=\dfrac{3}{10}.\dfrac{5}{9}\)
\(\Rightarrow x=\dfrac{1}{6}\)
\(\left(x+9\right)+\left(x-8\right)+\left(x+7\right)+\left(x-6\right)+\left(x+5\right)+\left(x-4\right)+\left(x+3\right)+\left(x-2\right)+\left(x+1\right)=95.9\\ =>x+9+x-8+x+7+x-6+x+5+x-4+x+3+x-2+x+1=855\\ =>\left(x+x+x+x+x+x+x+x+x\right)+\left(9-8+7-6+5-4+3-2+1\right)=855\\ =>9x+5=855\\ =>9x=855-5\\ =>9x=850\\ =>x=\dfrac{850}{9}\)
\(\left(x+9\right)+\left(x-8\right)+...+\left(x-2\right)+\left(x+1\right)\)
\(=x+9+x-8+...+x-2+x+1\)
\(=\left(x+9+x-8\right)+...+\left(x+5\right)+...+\left(x-2+x+1\right)\)
(Ta gộp 4 số vào 1 tổng, riêng (x+5) là ta giữ nguyên)
\(=\left(2x-1\right)+...+\left(x+5\right)+...+\left(2x-1\right)\)
\(=4\left(2x-1\right)+\left(x+5\right)\)
\(=8x-4+x-5\)
\(=9x-9\) (1)
Từ bài toán trên, ta có:
\(\left(x+9\right)+\left(x-8\right)+...+\left(x-2\right)+\left(x+1\right)=95,9\)
Từ (1)
\(\Leftrightarrow9x-9=95,9\)
\(9x=95,9-9\)
\(x=86,9:9\)
\(x=9,6\left(5\right)\)
\(x\times\dfrac{3}{5}=\dfrac{2}{3}+\dfrac{1}{3}\)
\(x\times\dfrac{3}{5}=\dfrac{3}{3}\)
\(x\times\dfrac{3}{5}=1\)
\(x=1:\dfrac{3}{5}\)
\(x=1\times\dfrac{5}{3}\)
\(x=\dfrac{5}{3}\)
\(x-\dfrac{4}{9}=\dfrac{3}{7}:\dfrac{9}{14}\)
\(x-\dfrac{4}{9}=\dfrac{3}{7}\times\dfrac{14}{9}\)
\(x-\dfrac{4}{9}=\dfrac{2}{3}\)
\(x=\dfrac{2}{3}+\dfrac{4}{9}\)
`x`\(=\dfrac{18}{27}+\dfrac{12}{27}\)
\(x=\dfrac{30}{27}=\dfrac{10}{9}\)
Câu 1: Tác phẩm Quốc âm thi tập là của ai ? (1đ)
a. Nguyễn Trãi.
b. Lê Thánh Tông.
c. Lý Tử Tấn.
d .Lương Thế Vinh.
1) \(\left(x-3\right)^2-4=0\)
\(\Leftrightarrow\left(x-3-2\right)\left(x-3+2\right)=0\)
\(\Leftrightarrow\left(x-5\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=1\end{matrix}\right.\)
2) \(x^2-2x=24\)
\(\Leftrightarrow x^2-2x-24=0\)
\(\Leftrightarrow x^2+4x-6x-24=0\)
\(\Leftrightarrow x\left(x+4\right)-6\left(x+4\right)=0\)
\(\Leftrightarrow\left(x+4\right)\left(x-6\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-4\end{matrix}\right.\)
1.
=3/5x(3/7+4/7)+2/5x(13/9-4/9)
=3/5x1+2/5x1
=3/5+2/5
=1
2.Xx(3/4+4/5)=7/10
Xx31/20=7/10
X =7/10:31/20
X =14/31
\(\frac{3}{5}\cdot\frac{3}{7}+\frac{3}{5}\cdot\frac{4}{7}+\frac{2}{5}\cdot\frac{13}{9}-\frac{2}{5}\cdot\frac{4}{9}\)
\(=\frac{3}{5}\cdot\left(\frac{3}{7}+\frac{4}{7}\right)+\frac{2}{5}\cdot\left(\frac{13}{9}-\frac{4}{9}\right)\)
\(=\frac{3}{5}\cdot1+\frac{2}{5}\cdot1\)\(=\frac{3}{5}+\frac{2}{5}=1\)
_________________________________________
\(\frac{3}{4}\cdot x+\frac{4}{5}\cdot x=\frac{7}{10}\)
\(\left(\frac{3}{4}+\frac{4}{5}\right)\cdot x=\frac{7}{10}\)
\(\frac{31}{20}\cdot x=\frac{7}{10}\)
\(x=\frac{7}{10}:\frac{31}{20}\)
\(x=\frac{14}{31}\)
a) 3/8 . x = 9/8 - 1
3/8 . x = 1/8
x = 1/8 : 3/8
x = 1/3
b) 4/5 . x = 7/5 - 1/5
4/5 . x = 6/5
x = 6/5 : 4/5
x = 3/2
c) 12/7 : x + 2/3 = 7/5
12/7 : x = 7/5 - 2/3
12/7 : x = 11/15
x = 12/7 : 11/15
x = 180/77
d) 3.(x + 7) - 15 = 27
3.(x + 7) = 27 + 15
3.(x + 7) = 42
x + 7 = 42 : 3
x + 7 = 14
x = 14 - 7
x = 7
a) \(\dfrac{3}{8}x=\dfrac{9}{8}-1\)
\(\Rightarrow\dfrac{3}{8}x=\dfrac{1}{8}\)
\(\Rightarrow x=\dfrac{1}{8}:\dfrac{3}{8}=\dfrac{1}{3}\)
b) \(\dfrac{4}{5}x=\dfrac{7}{5}-\dfrac{1}{5}\)
\(\Rightarrow\dfrac{4}{5}x=\dfrac{6}{5}\)
\(\Rightarrow x=\dfrac{6}{5}:\dfrac{4}{5}=\dfrac{3}{2}\)
c) \(\dfrac{12}{7}:x+\dfrac{2}{3}=\dfrac{7}{5}\)
\(\Rightarrow\dfrac{12}{7}:x=\dfrac{7}{5}-\dfrac{2}{3}\)
\(\Rightarrow\dfrac{12}{7}:x=\dfrac{11}{15}\)
\(\Rightarrow x=\dfrac{12}{7}:\dfrac{11}{15}=\dfrac{180}{77}\)
d) \(3\left(x+7\right)-15=27\)
\(\Leftrightarrow3\left(x+7\right)=42\)
\(\Leftrightarrow x+7=14\Leftrightarrow x=7\)
Giải
( x + 1 ) + ( x + 3 ) + ( x + 5 ) + ( x + 7 ) + ( x + 9 ) = 750
x x ( 1 + 3 + 5 + 7 + 9 ) = 750
x x 25 = 750
x = 750 : 25
x = 30
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