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AS
1
15 tháng 2 2020
\(A=\left|-x+8\right|-21\)
\(A=\left|-x+8\right|-21\ge-21\)
\(MinA=-21\Leftrightarrow-x+8=0\)\(\Leftrightarrow x=8\)
\(B=\left|-x-17\right|+\left|y-36\right|+12\)
\(B=\left|-x-17\right|+\left|y-36\right|+12\ge12\)
\(MinB=12\Leftrightarrow\hept{\begin{cases}-x-17=0\\y-36=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=-17\\y=36\end{cases}}\)
\(C=-\left|2x+8\right|-35\)
\(C=-\left|2x+8\right|-35\le-35\)
\(MaxC=-35\Leftrightarrow2x+8=0\Leftrightarrow x=-4\)
25 tháng 4 2017
Bài 1: a) Ta có : \(\dfrac{-3}{x}=\dfrac{x}{-27}\Leftrightarrow\left(-3\right).\left(-27\right)=x.x\Leftrightarrow81=x^2\Leftrightarrow9^2=x^2\Leftrightarrow x=9\)
b) Do \(\dfrac{2}{3}\) của x là -150 nên x là: (-150) : \(\dfrac{2}{3}\) = -225
c) \(\dfrac{2}{2.4}+\dfrac{2}{4.6}+...+\dfrac{2}{x\left(x+2\right)}=\dfrac{4}{9}\)
\(\Leftrightarrow\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+...+\dfrac{1}{x}-\dfrac{1}{x+2}=\dfrac{4}{9}\)
\(\Leftrightarrow\dfrac{1}{2}-\dfrac{1}{x+2}=\dfrac{4}{9}\)
\(\Leftrightarrow\dfrac{1}{x+2}=\dfrac{1}{2}-\dfrac{4}{9}\)
\(\Leftrightarrow\dfrac{1}{x+2}=\dfrac{1}{18}\)
\(\Leftrightarrow x+2=18\)
\(\Leftrightarrow x=16\)
Bài 2:
\(A=\left(\dfrac{1}{99}+\dfrac{12}{999}+\dfrac{123}{999}\right)\left(\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{6}\right)\)
\(A=\left(\dfrac{1}{99}+\dfrac{12}{999}+\dfrac{123}{999}\right)\left(\dfrac{1}{6}-\dfrac{1}{6}\right)\)
\(A=\left(\dfrac{1}{99}+\dfrac{12}{999}+\dfrac{123}{999}\right).0\)
\(A=0\)
NL
21 tháng 4 2017
\(\Leftrightarrow\)\(x-\left(\frac{13x}{18}-\frac{4}{18}\right)=\frac{4}{9}\)
\(\Leftrightarrow\)\(\frac{18x}{18}-\frac{13x}{18}+\frac{4}{18}=\frac{4}{9}\)
\(\Leftrightarrow\)\(\frac{5x}{18}=\frac{4}{9}-\frac{4}{18}\)
\(\Leftrightarrow\)\(\frac{5x}{18}=\frac{2}{9}\)
\(\Leftrightarrow\)\(5x=\frac{18.2}{9}\)
\(\Leftrightarrow\)\(5x=4\)
\(\Leftrightarrow\)\(x=\frac{4}{5}\)
KK
21 tháng 2 2019
a) (-12)2.x = 56 + 10.13x
=> 144.x = 56 + 130x
=> 144x - 130x = 56
=> 14x = 56
=>x = 56 : 14
=> x = 4
b) 80 - (x2 + 5) = 66
=> x2 + 5 = 80 - 66
=> x2 + 5 = 14
=> x2 = 14 - 5
=> x2 = 9
=> x2 = 32
=> \(\orbr{\begin{cases}x=3\\x=-3\end{cases}}\)
KK
21 tháng 2 2019
c) 9 - 25 = (7 - x) - (25 + 7)
=> -16 = (7 - x) - 32
=> 7 - x = -16 + 32
=> 7 - x = 16
=> x = 7 - 16
=> x = -9
d) \(\left(x+5\right)^2=16\)
=> \(\left(x+5\right)^2=4^2\)
=> \(\orbr{\begin{cases}x+5=4\\x+5=-4\end{cases}}\)
=> \(\orbr{\begin{cases}x=-1\\x=-9\end{cases}}\)
19 tháng 5 2017
a)
2 - x = 17 - (-5)
2 - x = 22
x = 2 - 22
x = (-20)
b)
b)x-12=-9-15
x-12=-24
x=(-24)+12
x=-12
HC
19 tháng 5 2017
a. \(2-x=17-\left(-5\right)\)
\(\Leftrightarrow2-x=22\)
\(\Leftrightarrow x=2-22\)
\(\Leftrightarrow x=-20\)
b. \(x-12=\left(-9\right)-15\)
\(\Leftrightarrow x-12=-24\)
\(\Leftrightarrow x=-24+12\)
\(\Leftrightarrow x=-12\)
\(=\left(2.\left(2^3\right)^4.\left(3^3\right)^2+2^2.\left(2.3\right)^9\right):\left(2^{12}.\left(3^2\right)^3.31\right)\)
\(=\left(2^{13}.3^6+2^{11}.3^9\right):\left(2^{12}.3^6.31\right)\)
\(=\left[2^{11}.3^6\left(2^2+3^3\right)\right]:\left(2^{12}.3^6.31\right)\)
\(=\frac{2^{11}.3^6.31}{2^{12}.3^6.31}=\frac{1}{2}\)
Đưa về phân số:
\(=\frac{2.8^4.27^2+4.6^9}{2^{12}.9^3.31}\)
\(=\frac{2.\left(2^3\right)^4.\left(3^3\right)^2+2^2.\left(2.3\right)^9}{2^{12}.\left(3^2\right)^3.31}\)
\(=\frac{2.2^{3.4}.3^{3.2}+2^2.2^9.3^9}{2^{12}.3^{2.3}.31}\)
\(=\frac{2.2^{12}.3^6+2^{2+9}.3^9}{2^{12}.3^6.31}\)
\(=\frac{2^{1+12}.3^6+2^{11}.3^9}{2^{12}.3^6.31}\)
\(=\frac{2^{13}.3^6+2^{11}.3^9}{2^{12}.3^6.31}\)
\(=\frac{2^{11}.3^6\left(2^2+3^3\right)}{2^{12}.3^6.31}\)
\(=\frac{2^{11}.3^6.31}{2^{12}.3^6.31}=\frac{1}{2}\)
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