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Lời giải:
a, \(\dfrac{12}{19}.\dfrac{7}{15}.\dfrac{-13}{17}.\dfrac{19}{12}.\dfrac{17}{13}\)
\(=\dfrac{12}{19}.\dfrac{-7}{15}.\dfrac{13}{17}.\dfrac{19}{12}.\dfrac{17}{13}\)
\(=\left(\dfrac{12}{19}.\dfrac{19}{12}\right).\left(\dfrac{13}{17}.\dfrac{17}{13}\right).\dfrac{-7}{15}\)
\(=1.1.\dfrac{-7}{15}\)
\(=\dfrac{-7}{15}\)
b, \(\dfrac{a}{27}=\dfrac{-5}{9}=\dfrac{-45}{b}\)
\(\Rightarrow\left\{{}\begin{matrix}\dfrac{a}{27}=\dfrac{-5}{9}\\\dfrac{-45}{b}=\dfrac{-5}{9}\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}9a=-5.27\\-5b=-45.9\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}9a=-135\\-5b=-405\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a=-15\\b=-81\end{matrix}\right.\)
Vậy, \(a=-15;b=-81\).
a) 7.28=x.x
=> 196=x2
=> \(\left(\pm14\right)^2=x^2\)
=> x=\(\pm14\)
b) DK: x≠-17
pt<=> 4.(10+2)=6.(17+x)
=> 4.12=17.6+6x
=> 48-102=6x
=>-66=6x
=>x=-11
c) 7.(x+40)=6.(17+x)
=> 7x+280=102+6x
=> 7x-6x=102-280
=> x=-178
Giải:
a) \(\dfrac{7}{x}=\dfrac{x}{28}\)
\(\Leftrightarrow x^2=196\)
\(\Leftrightarrow x=\pm\sqrt{196}=\pm14\)
Vậy ...
b) \(\dfrac{10+2}{17+x}=\dfrac{3}{4}\)
\(\Leftrightarrow40+8=51+3x\)
\(\Leftrightarrow3x=40+8-51=-3\)
\(\Leftrightarrow x=-\dfrac{3}{3}=-1\)
Vậy ...
c) \(\dfrac{40+x}{17+x}=\dfrac{6}{7}\)
\(\Leftrightarrow280+7x=102+6x\)
\(\Leftrightarrow7x-6x=102-280\)
\(\Leftrightarrow x=-178\)
Vậy ...
1. \(\dfrac{16.17-5}{16.16-1}:\left(x-\dfrac{2}{3}\right)=\dfrac{1}{3}\)
<=> \(\dfrac{272-5}{256-1}:\left(x-\dfrac{2}{3}\right)=\dfrac{1}{3}\)
<=> \(\dfrac{267}{255}:\left(x-\dfrac{2}{3}\right)=\dfrac{1}{3}\)
<=> x - \(\dfrac{2}{3}=\dfrac{267}{85}\)
<=> x = \(\dfrac{971}{255}\)
@Triều Nguyễn Quốc
2. a, 8\(\dfrac{1}{5}\left(11\dfrac{94}{1591}-6\dfrac{38}{1517}\right):8\dfrac{11}{13}\)
= \(\dfrac{41}{5}\left(5\dfrac{60}{1763}\right):\dfrac{355}{43}\)
= \(\dfrac{41}{5}.\dfrac{8875}{1763}:\dfrac{355}{43}\)
= \(\dfrac{1775}{43}:\dfrac{355}{43}\)
= 5
@Triều Nguyễn Quốc
Gọi số được thêm vào là x
Theo đề ta có : \(\dfrac{13+x}{19+x}=\dfrac{5}{7}\)
\(\Rightarrow7\cdot\left(13+x\right)=5\cdot\left(19+x\right)\)
\(\Leftrightarrow91+7x=95+5x\)
\(\Leftrightarrow-4=-2x\)
\(\Rightarrow x=\dfrac{-4}{-2}=2\)
Vậy số tự nhiên cần thêm vào là 2.
Bài 2:
\(\dfrac{7}{3\cdot4}-\dfrac{9}{4\cdot5}+\dfrac{11}{5\cdot6}-\dfrac{13}{6\cdot7}+\dfrac{15}{7\cdot8}-\dfrac{17}{8\cdot9}+\dfrac{19}{9\cdot10}\)
\(=\dfrac{1}{3}+\dfrac{1}{4}-\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}+\dfrac{1}{6}-\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{9}+\dfrac{1}{10}\)
=1/3+1/10
=13/30
a, \(x+\dfrac{2}{3}=0,2\)
\(\Rightarrow x+\dfrac{2}{3}=\dfrac{1}{5}\)
\(\Rightarrow x=\dfrac{1}{5}-\dfrac{2}{3}\)
\(\Rightarrow x=\dfrac{-7}{10}\)
b, \(\dfrac{17}{7}-\dfrac{6}{5}x=\dfrac{17}{4}\)
\(\Rightarrow\dfrac{6}{5}x=\dfrac{17}{7}-\dfrac{17}{4}\)
\(\Rightarrow\dfrac{6}{5}x=\dfrac{-51}{28}\)
\(\Rightarrow x=\dfrac{-51}{28}:\dfrac{6}{5}\)
\(\Rightarrow x=\dfrac{-85}{56}\)
\(40.\dfrac{6}{17}=\dfrac{240}{17}\)
K/quả ra dạng số mà như thế thì viết dạng p/s tối giản cho nhanh=))
gì mà ảo vậy =))))
@
32 Nguyễn Thanh Quang t toàn làm thế-))