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Giải:
a) \(\dfrac{-5}{8}=\dfrac{x}{16}\)
\(\Rightarrow x=\dfrac{16.-5}{8}=-10\)
\(\dfrac{3x}{9}=\dfrac{2}{6}\)
\(\Rightarrow3x=\dfrac{2.9}{6}=3\)
\(\Rightarrow x=1\)
b) \(\dfrac{x+3}{15}=\dfrac{1}{3}\)
\(\Rightarrow x+3=\dfrac{1.15}{3}=5\)
\(\Rightarrow x=2\)
\(\dfrac{6}{2x+1}=\dfrac{2}{7}\)
\(\Rightarrow2x+1=\dfrac{6.7}{2}=21\)
\(\Rightarrow x=10\)
c) \(\dfrac{4}{x-6}=\dfrac{y}{24}=\dfrac{-12}{18}\)
\(\Rightarrow\dfrac{4}{x-6}=\dfrac{-12}{18}\)
\(\Rightarrow x-6=\dfrac{18.4}{-12}=-6\)
\(\Rightarrow x=0\)
\(\Rightarrow\dfrac{y}{24}=\dfrac{-12}{18}\)
\(\Rightarrow y=\dfrac{-12.24}{18}=-16\)
\(\dfrac{3-x}{-12}=\dfrac{16}{y+1}=\dfrac{192}{-72}\)
\(\Rightarrow\dfrac{3-x}{-12}=\dfrac{192}{-72}\)
\(\Rightarrow3-x=\dfrac{192.-12}{-72}=32\)
\(\Rightarrow x=-29\)
\(\Rightarrow\dfrac{16}{y+1}=\dfrac{192}{-72}\)
\(\Rightarrow y+1=\dfrac{16.-72}{192}=-6\)
d) \(\dfrac{-2}{3}< \dfrac{x}{5}< \dfrac{-1}{6}\)
\(\Rightarrow\dfrac{-20}{30}< \dfrac{6x}{30}< \dfrac{-5}{30}\)
\(\Rightarrow6x\in\left\{-18;-12;-6\right\}\)
\(\Rightarrow x\in\left\{-3;-2;-1\right\}\)
\(\dfrac{-1}{5}\le\dfrac{x}{8}\le\dfrac{1}{4}\)
\(\Rightarrow\dfrac{-8}{40}\le\dfrac{5x}{40}\le\dfrac{10}{40}\)
\(\Rightarrow5x\in\left\{-5;0;5;10\right\}\)
\(\Rightarrow x\in\left\{-1;0;1;2\right\}\)
e) \(\dfrac{x+46}{20}=x\dfrac{2}{5}\)
\(\Rightarrow\dfrac{x+46}{20}=x+\dfrac{2}{5}\)
\(\Rightarrow\dfrac{x+46}{20}=\dfrac{5x+2}{5}\)
\(\Rightarrow5.\left(x+46\right)=20.\left(5x+2\right)\)
\(\Rightarrow5x+230=100x+40\)
\(\Rightarrow5x-100x=40-230\)
\(\Rightarrow-95x=-190\)
\(\Rightarrow x=-190:-95\)
\(\Rightarrow x=2\)
\(y\dfrac{5}{y}=\dfrac{86}{y}\)
\(\Rightarrow y+\dfrac{5}{y}=\dfrac{86}{y}\)
\(\Rightarrow\dfrac{y^2+5}{y}=\dfrac{86}{y}\)
\(\Rightarrow y^2+5=86\)
\(\Rightarrow y^2=86-5\)
\(\Rightarrow y^2=81\)
\(\Rightarrow\left[{}\begin{matrix}y=9\\y=-9\end{matrix}\right.\)
Chúc bạn học tốt!
a, 3x ( y+1) + y + 1 = 7
(y+1)(3x +1) =7
th1 : \(\left\{{}\begin{matrix}y+1=1\\3x+1=7\end{matrix}\right.\) => \(\left\{{}\begin{matrix}y=0\\x=2\end{matrix}\right.\)
th2: \(\left\{{}\begin{matrix}y+1=-1\\3x+1=-7\end{matrix}\right.\)=> x = -8/3 (loại)
th3: \(\left\{{}\begin{matrix}y+1=7\\3x+1=1\end{matrix}\right.\)=> \(\left\{{}\begin{matrix}y=6\\x=0\end{matrix}\right.\)
th 4 : \(\left\{{}\begin{matrix}y+1=-7\\3x+1=-1\end{matrix}\right.\)=> x=-2/3 (loại)
Vậy (x,y)= (2 ;0); (0; 6)
b, xy - x + 3y - 3 = 5
(x( y-1) + 3( y-1) = 5
(y-1)(x+3) = 5
th1: \(\left\{{}\begin{matrix}y-1=1\\x+3=5\end{matrix}\right.\) => \(\left\{{}\begin{matrix}y=2\\x=8\end{matrix}\right.\)
th2: \(\left\{{}\begin{matrix}y-1=-1\\x+3=-5\end{matrix}\right.\) => \(\left\{{}\begin{matrix}y=0\\x=-8\end{matrix}\right.\)
th3: \(\left\{{}\begin{matrix}y-1=5\\x+3=1\end{matrix}\right.\) => \(\left\{{}\begin{matrix}y=6\\x=-2\end{matrix}\right.\)
th4: \(\left\{{}\begin{matrix}y-1=-5\\x+3=-1\end{matrix}\right.\) => \(\left\{{}\begin{matrix}y=-4\\x=-4\end{matrix}\right.\)
vậy (x, y) = ( 8; 2); ( -8; 0); (-2; 6); (-4; -4)
c, 2xy + x + y = 7 => y = \(\dfrac{7-x}{2x+1}\) ; y ϵ Z ⇔ 7-x ⋮ 2x+1
⇔ 14 - 2x ⋮ 2x + 1 ⇔ 15 - 2x - 1 ⋮ 2x + 1
th1 : 2x + 1 = -1=> x = -1; y = \(\dfrac{7-(-1)}{-1.2+1}\) = -8
th2: 2x+ 1 = 1=> x =0; y = 7
th3: 2x+1 = -3 => x = x=-2 => y = \(\dfrac{7-(-2)}{-2.2+1}\) = -3
th4: 2x+ 1 = 3 => x = 1 => y = \(\dfrac{7+1}{2.1+1}\) = 2
th5: 2x + 1 = -5 => x = -3=> y = \(\dfrac{7-(-3)}{-3.2+1}\) = -2
th6: 2x + 1 = 5 => x = 2; ; y = \(\dfrac{7-2}{2.2+1}\) =1
th7 : 2x + 1 = -15 => x = -8; y = \(\dfrac{7-(-8)}{-8.2+1}\) = -1
th8 : 2x+1 = 15 => x = 7; y = \(\dfrac{7-7}{2.7+1}\) = 0
kết luận
(x,y) = (-1; -8); (0 ;7); ( -2; -3) ; ( 1; 2); ( -3; -2); (2;1); (-8;-1);(7;0)
3xy−2x+5y=293xy−2x+5y=29
9xy−6x+15y=879xy−6x+15y=87
(9xy−6x)+(15y−10)=77(9xy−6x)+(15y−10)=77
3x(3y−2)+5(3y−2)=773x(3y−2)+5(3y−2)=77
(3y−2)(3x+5)=77(3y−2)(3x+5)=77
⇒(3y−2)⇒(3y−2) và (3x+5)(3x+5) là Ư(77)=±1,±7,±11,±77Ư(77)=±1,±7,±11,±77
Ta có bảng giá trị sau:
Do x,y∈Zx,y∈Z nên (x,y)∈{(−4;−3),(−2;−25),(2;3),(24;1)}
a: =>-2x=90/91
hay x=-45/91
b: =>2x=-7
hay x=-7/2
c: ->-3x=-12
hay x=4
\(a,3x\left(y+1\right)+\left(y+1\right)=7\\ =>\left(3x+1\right)\left(y+1\right)=7\)
\(+,TH1:\left\{{}\begin{matrix}3x+1=1\\y+1=7\end{matrix}\right.=>\left\{{}\begin{matrix}x=0\\y=6\end{matrix}\right.\\ +,TH2:\left\{{}\begin{matrix}3x+1=7\\y+1=1\end{matrix}\right.=>\left\{{}\begin{matrix}x=2\\y=0\end{matrix}\right.\\ +,TH3:\left\{{}\begin{matrix}3x+1=\left(-1\right)\\y+1=\left(-7\right)\end{matrix}\right.=>\left\{{}\begin{matrix}x=-\dfrac{2}{3}\\y=-8\end{matrix}\right.\\ +,TH4:\left\{{}\begin{matrix}3x+1=-7\\y+1=-1\end{matrix}\right.=>\left\{{}\begin{matrix}x=-\dfrac{8}{3}\\y=-2\end{matrix}\right.\)
a) Vì x, y thuộc Z mà (x-1) (y-2) = 7
=> 7 chia hết cho x - 1; y - 2
=> x - 1; y - 2 thuộc Ư (7) = { -1; 1; -7; 7 }
Ta có :
| x-1 | -7 | -1 | 1 | 7 |
| y-2 | -1 | -7 | 7 | 1 |
| x | -6 | 0 | 2 | 8 |
| y | 1 | -5 | 9 | 3 |
Vậy các cặp x, y thỏa mãn là : x =-6,y=1 ; x=0,y=-5 ; x=2,y=9 ; x=8,y=3
Làm tương tự vs các câu còn lại
\(\left(x-1\right)\left(y-2\right)=7\)
\(\Rightarrow x-1;y-2\inƯ\left(7\right)\)
\(Ư\left(7\right)=\left\{1;-1;7;-7\right\}\)
Ta có bảng sau :
| x - 1 | 1 | - 1 | 7 | - 7 |
| x | 2 | 0 | 8 | - 6 |
| y - 2 | 1 | - 1 | 7 | - 7 |
| y | 3 | 1 | 9 | - 5 |
Vậy ..........
a: \(\Leftrightarrow\left(x;y-3\right)\in\left\{\left(1;17\right);\left(17;1\right);\left(-1;-17\right);\left(-17;-1\right)\right\}\)
=>\(\left(x,y\right)\in\left\{\left(1;20\right);\left(17;4\right);\left(-1;-14\right);\left(-17;2\right)\right\}\)
b: \(\Leftrightarrow\left(x-1;y+2\right)\in\left\{\left(1;7\right);\left(7;1\right);\left(-1;-7\right);\left(-7;-1\right)\right\}\)
=>\(\left(x,y\right)\in\left\{\left(2;5\right);\left(8;-1\right);\left(0;-9\right);\left(-6;-3\right)\right\}\)
c: =>(y+1)(3x+1)=7
=>\(\left(3x+1;y+1\right)\in\left\{\left(1;7\right);\left(7;1\right)\right\}\)
=>\(\left(x,y\right)\in\left\{\left(0;6\right);\left(2;0\right)\right\}\)