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2.(x-3)+5.(x+4)=49
2x-6+5x+20=49
2x+5x=49-20+6=35
7x=35
x=\(\dfrac{35}{7}\)=5
vậy
2 ( x – 3 ) + 5 ( x + 4 ) = 49
2x - 6 + 5x + 20 = 49
7x + 14 = 49
7x = 35
x = 5
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Câu 6: Khôg có cau nào đúng
Câu 7: C
Câu 8: B
Câu 9: B
Câu 10: D
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\(\dfrac{4}{x}=\dfrac{y}{21}=\dfrac{28}{49}=\dfrac{28:7}{49:7}=\dfrac{4}{9}\\ Vậy:x=\dfrac{4.9}{4}=9\\ y=\dfrac{4.21}{9}=\dfrac{28}{3}\)
\(\dfrac{x}{2}=\dfrac{3}{y}\\ \Leftrightarrow x.y=2.3=6\\ Vậy:\left[{}\begin{matrix}\left(x;y\right)=\left(1;6\right)=\left(6;1\right)\\\left(x;y\right)=\left(2;3\right)=\left(3;2\right)\end{matrix}\right.\)
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3.|x+1|-2=4
3.|x+1|=4+2
3.|x+1|=6
|x+1|=6:3
|x+1|=2
Trường hợp 1 x+1=2
x=2-1
x=1
trường hợp 2
x+1=-2
x=(-2)-1
x=-3
==> x thuộc {1; -3}
k mk nha chúc học tốt
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\(\frac{x}{2}=\frac{y}{3};\frac{y}{5}=\frac{z}{4}\)\(\Leftrightarrow\frac{x}{10}=\frac{y}{15};\frac{y}{15}=\frac{z}{12}\Leftrightarrow\)\(\frac{x}{10}=\frac{y}{15}=\frac{z}{12}\)
\(\Rightarrow\frac{x-y+z}{10-15+12}=-\frac{49}{7}=-7\)
\(\Rightarrow x=-7.10=-70\)
\(y=-7.15=-105\)
\(z=-7.12=-84\)
Tìm x biết: 2 ( x - 3 ) + 5 ( x + 4 ) = 49
<=> 2x - 6 + 5x +20 = 49
<=> 2x+ 5x = 49 + 6 -20
<=> 7x = 35
<=> x = 35:7
<=> x = 5
x = 5 nha