1.tính hợp lý:
-1999.19981998 + 19991999.1998
2.tìm x
A) -1-2(-3+2
Nhanh nhé mk tick
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a) -1 - 2(-3 + 2|x|) = -7
=> 2(-3 + 2|x|) = -1 + 7
=> 2(-3 + 2|x|) = 6
=> -3 + 2|x| = 6 : 2
=> -3 + 2|x| = 3
=> 2|x| = 3 + 3
=> 2|x| = 6
=> |x| = 6 : 2
=> |x| = 3
=> \(\orbr{\begin{cases}x=3\\x=-3\end{cases}}\)
=> x = 0
Vậy ...
(13.3x - 3x) : 2 = 162
=> (13 - 1).3x = 162 . 2
=> 12.3x = 324
=> 3x = 324 : 12
=> 3x = 27
=> 3x = 33
=> x = 3
Vậy ...
\(\text{Ta có: 10/7 x 2/3 + 6/5 : 3/10 - 2/3 x 3/7 = 10/7 x 2/3 + 4 - 2/3 x 3/7
}\)
\(\text{ = 2/3 x ( 10/7 - 3/7) + 4
}\)
\(\text{= 2/3 x 1 + 4}\)
\(\text{ = 2/3 + 12/3
}\)
\(\text{ = 14/3}\)
Ta có:
10/7 x 2/3 + 6/5 : 3/10 - 2/3 x 3/7
= (10/7 - 3/7) x 2/3 + 6/5 : 3/10
= 1 x 2/3 + 4
= 2/3 + 4
= \(4\frac{2}{3}\)
Đáp số: \(4\frac{2}{3}\)
\(a,x+\dfrac{2}{5}=\dfrac{1}{2}\)
\(x=\dfrac{1}{2}-\dfrac{2}{5}\)
\(x=\dfrac{5}{10}-\dfrac{4}{10}\)
\(\Rightarrow x=....\)
\(a,x+\dfrac{2}{5}=\dfrac{1}{2}\\ \Rightarrow x=\dfrac{1}{2}-\dfrac{2}{5}=\dfrac{5-4}{10}=\dfrac{1}{10}\)
\(b,x-\dfrac{2}{5}=\dfrac{1}{7}\\ \Rightarrow x=\dfrac{1}{7}+\dfrac{2}{5}=\dfrac{5+14}{35}=\dfrac{19}{35}\)
\(c,x\cdot\dfrac{3}{4}=\dfrac{9}{20}\\ \Rightarrow x=\dfrac{9}{20}:\dfrac{3}{4}=\dfrac{9}{20}\cdot\dfrac{4}{3}=\dfrac{3\cdot1}{5\cdot1}=\dfrac{3}{5}\)
\(d,x:\dfrac{1}{7}=14\\ \Rightarrow x=14\cdot\dfrac{1}{7}=\dfrac{14}{7}=2\)
\(e,\dfrac{2}{3}-x=\dfrac{1}{5}\\ \Rightarrow x=\dfrac{2}{3}-\dfrac{1}{5}=\dfrac{10-3}{15}=\dfrac{7}{15}\)
\(f,\dfrac{4}{15}:x=\dfrac{12}{25}\\ \Rightarrow x=\dfrac{4}{15}:\dfrac{12}{25}=\dfrac{4}{15}\cdot\dfrac{25}{12}=\dfrac{1\cdot5}{3\cdot3}=\dfrac{5}{9}\)
(13.3x-2-3x):2=162
<=>3x-2(13-32)=162.2
<=>3x-2.4=324
<=>3x-2=324:4
<=>3x-2=81=34
<=>x-2=4
<=>x=6
Vậy...
Ta có: \(\left(13.3^{x-2}-3^x\right)\div2=162\)
\(\Leftrightarrow13.3^{x-2}-3^{x-2+2}=162.2\)
\(\Leftrightarrow13.3^{x-2}-3^2.3^{x-2}=324\)
\(\Leftrightarrow\left(13-9\right).3^{x-2}=324\)
\(\Leftrightarrow4.3^{x-2}=324\)
\(\Leftrightarrow3^{x-2}=\dfrac{324}{4}=81=3^4\)
\(\Leftrightarrow3^{x-2}=3^4\Leftrightarrow x-2=4\Leftrightarrow x=6\)
Vậy \(x=6\)