tìm x biết
a,\(\frac{x}{3}=\frac{y}{5}vày-x=8\)8
\(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}vày-2z+3x=14\)
Tìm x; y; z
đặt \(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}=k\)
=> x= 3k
y=8k
z=5k
ta có : y-2z+3x=14
8k-10k+9k=14
k(8-10+9)=14
k7=14
=> k=2
vậy x= 6;y=16;z=10
cách khác :
\(\frac{x}{3}=\frac{y}{8}=\frac{z}{5}=>\)\(\frac{3x}{9}=\frac{y}{8}=\frac{2z}{10}\)\(=\frac{y-2z+3x}{8-10+9}\)\(=\frac{14}{7}=2\)
=> x= 6;y=16;z=10
1) \(\frac{24}{-12}=\frac{x}{5}=\frac{-y}{3}\)Tìm x và y
2) \(\frac{1}{3}+\frac{-2}{5}+\frac{1}{6}+\frac{-5}{25}\le\frac{x}{10}< \frac{-3}{4}+\frac{4}{14}+\frac{-2}{8}+\frac{-3}{5}+\frac{5}{7}\)Tìm x
3) \(\frac{8.x+18}{2.x+6}\)Tìm x
Bài 1 : Tính :
B = \(\frac{\frac{1}{2}+\frac{3}{4}-\frac{5}{6}}{\frac{1}{4}+\frac{3}{8}-\frac{5}{12}}+\frac{\frac{3}{4}+\frac{3}{5}-\frac{3}{8}}{\frac{1}{4}+\frac{1}{5}-\frac{1}{8}}\)
Bài 2 : tìm x và y
a) x3 - 36x = 0
b) \(\frac{x-3}{y-2}=\frac{3}{2}\)và x - y = 4 ( x , y \(\in\)Z )
Bài 1:
\(B=\frac{\frac{1}{2}+\frac{3}{4}-\frac{5}{6}}{\frac{1}{4}+\frac{3}{8}-\frac{5}{12}}+\frac{\frac{3}{4}+\frac{3}{5}-\frac{3}{8}}{\frac{1}{4}+\frac{1}{5}-\frac{1}{8}}\)\(=\frac{\frac{1}{2}+\frac{3}{4}-\frac{5}{6}}{\frac{1}{2}\left(\frac{1}{2}+\frac{3}{4}-\frac{5}{6}\right)}+\frac{3\left(\frac{1}{4}+\frac{1}{5}-\frac{1}{8}\right)}{\frac{1}{4}+\frac{1}{5}-\frac{1}{8}}\)
\(=\frac{1}{\frac{1}{2}}+3\) \(=2+3\) \(=5\)
Vậy B=5
Bài 2:
a) x3 - 36x = 0
=> x(x2-36)=0
=> x(x2+6x-6x-36)=0
=> x[x(x+6)-6(x+6) ]=0
=> x(x+6)(x-6)=0
\(\Rightarrow\orbr{\begin{cases}^{x=0}x+6=0\\x-6=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}^{x=0}x=-6\\x=6\end{cases}}\)
Vậy x=0; x=-6; x=6
b) (x - y = 4 => x=4+y)
x−3y−2 =32
=>2(x-3) = 3(y-2)
=>2x-6= 3y-6
=>2x-3y=0
=>2(4+y)-3y=0
=>8+2y-3y=0
=>8-y=0
=>y=8 (thỏa mãn)
Do đó x=4+y=4+8=12 (thỏa mãn)
Vậy x=12 và y =8
B= 1/2 + 3/4 - 5/6/1/2(1.2 + 3/4 - 5/6) + 3(1/4+ 1/5 - 1/8)/ 1/4 1/5 - 1/8
B= 1/ 1/2 + 3
B= 2+3
B=5
B2:
a) x^3 - 36x = 0
x(x^2 - 36) = 0
=> x=0 hoặc x^2-36=0
=> x= 0 hoặc x^2=36
=> x=0 hoặc x= +- 6
b) x-y = 4 => x= 4+y
thay x=4+y vào x- 3/ y-2=3/2, có:
4+y-3/ y+2 = 3/2
y+1/ y+2 = 3/2
y+2 -1/ y+2 = 3/2
1 - 1/y+2 = 3/2
1/y+2= 1-3/2
1/y+2 = -1/2
=> y+2 = -2
=> y= -4
Dp x= 4+y => x= 4-4
=> x=0
Vậy x=0 và y=-4
tìm x biết
a) \(\dfrac{x}{2}\)=\(\dfrac{y}{5}\) và x+y=-14
b)\(\dfrac{x}{7}=\dfrac{y}{5}\) và x-y=8
\(a.\)
\(\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{x+y}{2+5}=\dfrac{-14}{7}=-2\)
\(\Rightarrow\left\{{}\begin{matrix}x=\left(-2\right)\cdot2=-4\\y=\left(-2\right)\cdot5=-10\end{matrix}\right.\)
\(b.\)
\(\dfrac{x}{7}=\dfrac{y}{5}=\dfrac{x-y}{7-5}=\dfrac{8}{2}=4\)
\(\Rightarrow\left\{{}\begin{matrix}x=4\cdot7=28\\y=5\cdot4=20\end{matrix}\right.\)
tìm x,y,z biết
\(\frac{3}{8}x=\frac{4}{5}y=\frac{8}{7}z\)và x+y-z=73
Ta có:
\(\frac{3}{8}x=\frac{4}{5}y=\frac{8}{7}z\)
\(\Leftrightarrow\frac{3x}{8}=\frac{4y}{5}=\frac{8z}{7}\)
\(\Leftrightarrow\frac{x}{\frac{8}{3}}=\frac{y}{\frac{5}{4}}=\frac{z}{\frac{7}{8}}\)
Áp dụng tính chất dã tỉ số bằng nhau ta được:
\(\frac{x}{\frac{8}{3}}=\frac{y}{\frac{5}{4}}=\frac{z}{\frac{7}{8}}=\frac{x+y-z}{\frac{8}{3}+\frac{5}{4}-\frac{7}{8}}=\frac{73}{\frac{73}{24}}=24\)
\(\Rightarrow\hept{\begin{cases}x=24.\frac{8}{3}=64\\y=24.\frac{5}{4}=30\\z=24.\frac{7}{8}=21\end{cases}}\)
Vậy .......
\(\frac{2}{\left(x+1\right)\left(x+3\right)}+\frac{5}{\left(x+3\right)+\left(x+8\right)}+\frac{10}{\left(x+8\right)\left(x+18\right)}+\frac{1}{x+18}=\frac{5}{6}\)
Tìm x;y;z
tìm x :
\(\frac{5}{8}.8^{x+2}-\frac{3}{5}.8^x=\frac{5}{3}.8^{11}-\frac{3}{5}.8^9\)
Tìm x,y,z biết:
\(\frac{x}{5}=\frac{x+y}{8}=\frac{x+y-2z}{4}=3\)
Từ \(\frac{x}{5}=3\Rightarrow x=15\)
\(\frac{15+y}{8}=3\Rightarrow y=9\)
\(\frac{15+9-2z}{4}=3\Rightarrow z=6\)
\(\frac{x}{5}\)=3=\(\frac{15}{5}\)=>x=15
\(\frac{x+y}{8}\)=3=\(\frac{24}{8}\)=>x+y=24 =>15+y=24=>y=9
\(\frac{x+y-2z}{4}\)=3=\(\frac{12}{4}\)=>x+y-2z=12=>15+9-2z=12=>24-2z=12=>2z=24-12=12
=>z=6
vậy các số x,y,z=15,9,6
Câu 4. Tìm số nguyên x, biết
a) 8.x = 64
b) (-5).x = 25
c) 4.x+1+ 21
d) (-3).x -1= 8
`a, 8x=64`
`=>x= 64:8`
`=> x=8`
`b, (-5)x=25`
`=>x=25:(-5)`
`=>x=-5`
`c,4x+1=21`
`=>4x=21-1`
`=>4x=20`
`=>x=20:4`
`=>x=5`
`d, (-3)x-1=8`
`=>(-3)x=8+1`
`=>(-3)x=9`
`=>x=9:(-3)`
`=>x=(-3)`