84/91=12/x
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a 3.x-2.x=84-24
x=60
b 12x-91=3636:36
12x-91=101
12x=101+91
12x=192
x=192:12=16
25 + ( x - 15 ) = 30
x - 15 = 30 - 25
x = 5 + 15
x = 20
91 . 25 - 91 . 13 - 91 . 12
= 91. ( 25 - 13 -12 )
= 91. 0
= 0
64 . 16 + 81 . 84 + 17 . 16
= 16. ( 64 + 17 ) + 81 . 84
= 16 . 81 + 81 . 84
= 81 . ( 84 + 16 )
= 81 . 100
= 8100
~HT~ and ~ T.i.c.k ~
a. \(204-84:12\)
\(=204-7\)
\(=197\)
b. \(99-97+95-93+91-89+...+7-5+3-1\)
\(=\left(99-97\right)+\left(95-93\right)+\left(91-89\right)+...+\left(7-5\right)+\left(3-1\right)\)
\(=2+2+2+...+2+2\)
\(=2.25\)
\(=50\)
a: =-45-91+17-45+91
=-90+17=-73
b: =-57-84-31+57+84-31
=-31-31=-62
a) \(-\left(45+91\right)-\left(-17+45-91\right)\)
\(=-45-91+17-45+91\)
\(=17+-\left(45+45\right)-\left(91-91\right)\)
\(=17-90-0\)
\(=-73\)
b) \(\left(-57-84\right)-\left(31-57\right)-\left(-84+31\right)\)
\(=-57-84-31+57+84-31\)
\(=\left(-57+57\right)-\left(84-84\right)+\left(-31+-31\right)\)
\(=0+0-62\)
\(=-62\)
a)
\(\dfrac{111}{37}=3< x< \dfrac{91}{13}=7\)
Vậy x = {4;5;6}
b)
\(-\dfrac{84}{14}=-6< 3x< \dfrac{108}{9}=12\Leftrightarrow-2< x< 4\)
Vậy x = {-1;0;1;2;3}
a, Ta có : \(\dfrac{111}{37}< x< \dfrac{91}{13}\)
\(\Rightarrow3< x< 7\)
Mà x là số nguyên .
\(\Rightarrow x\in\left\{4;5;6\right\}\)
b, Ta có : \(-\dfrac{84}{14.3}< x< \dfrac{108}{9.3}\)
\(\Rightarrow-2< x< 4\)
Mà x là số nguyên .
\(\Rightarrow x\in\left\{-1;0;1;2;3\right\}\)
a: \(\dfrac{-13}{40}< \dfrac{-12}{40}\)
\(\dfrac{-5}{6}>\dfrac{-91}{104}\)
1)111/37<x<91/13
\(\Leftrightarrow\)\(\frac{1443}{481}\)<x<\(\frac{3367}{481}\)
vậy x\(\in\)\(\left\{\frac{1444}{481};......;\frac{3366}{481}\right\}\)
2)-84/14<x<108/9
\(\Leftrightarrow\)\(\frac{-801}{126}\)<x<\(\frac{432}{126}\)
vậy x\(\in\)\(\left\{\frac{-800}{126};.......;\frac{431}{126}\right\}\)
3)\(\frac{-x}{4}\)=\(\frac{-9}{x}\)\(\Rightarrow\)-x.x=(-x)2=4.(-9)=-36
\(\Rightarrow\)(-x)2=-36=(-6)2
vậy -x=6;x=6
\(\dfrac{84}{91}=\dfrac{12}{x}\)
\(\dfrac{12}{13}=\dfrac{12}{x}\)
=> \(x=13\)