Tìm x:
Cau a: -12.(x-5)+7(3-x)=5
Câu b: | x | <3, x< Z
câu c: (x-3).(x-5) < 0, x thuoc Z
câu d: (x-2).(x+4)=0
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Câu 30:
\(\dfrac{x+1}{8}=\dfrac{2}{x+1}\)
=>\(\left(x+1\right)^2=2\cdot8=16\)
=>\(\left[{}\begin{matrix}x+1=4\\x+1=-4\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=3\\x=-5\end{matrix}\right.\)
=>Chọn D
Câu 31:
\(-\dfrac{7}{15}\cdot\dfrac{5}{8}\cdot\dfrac{15}{-7}\cdot\left(-16\right)\)
\(=\dfrac{5}{8}\cdot\left(-16\right)=-10\)
=>Chọn D
Bài 1:
a) \(\dfrac{9}{20}-\dfrac{8}{15}\times\dfrac{5}{12}\)
\(=\dfrac{9}{20}-\dfrac{2}{9}\)
\(=\dfrac{41}{180}\)
b) \(\dfrac{2}{3}\div\dfrac{4}{5}\div\dfrac{7}{12}\)
\(=\dfrac{2}{3}\times\dfrac{5}{4}\times\dfrac{12}{7}\)
\(=\dfrac{5}{6}\times\dfrac{12}{7}\)
\(=\dfrac{10}{7}\)
c) \(\dfrac{7}{9}\times\dfrac{1}{3}+\dfrac{7}{9}\times\dfrac{2}{3}\)
\(=\dfrac{7}{9}\times\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\)
\(=\dfrac{7}{9}\times1\)
\(=\dfrac{7}{9}\)
Bài 2:
a) \(2\times\left(x-1\right)=4026\)
\(\left(x-1\right)=4026\div2\)
\(x-1=2013\)
\(x=2014\)
Vậy: \(x=2014\)
b) \(x\times3,7+6,3\times x=320\)
\(x\times\left(3,7+6,3\right)=320\)
\(x\times10=320\)
\(x=320\div10\)
\(x=32\)
Vậy: \(x=32\)
c) \(0,25\times3< 3< 1,02\)
\(\Leftrightarrow0,75< 3< 1,02\) ( S )
=> \(0,75< 1,02< 3\)
***c,4(x-5)-3(x+7)=-19
Suy ra (4x-20)-(3x+21)=-19
Suy ra (4x-3x)-(20+21)=-19
Suy ra x-41=-19
suy ra x=-19+41
Suy ra x=22
Vậy x=22
a: =>x-4/5=5/8
=>x=5/8+4/5=57/40
b: 7-x=5/12
=>x=7-5/12=79/12
a, x - \(\dfrac{3}{5}\) = \(\dfrac{5}{8}\) + \(\dfrac{1}{5}\)
x - \(\dfrac{3}{5}=\dfrac{33}{40}\)
x= \(\dfrac{33}{40}+\dfrac{3}{5}\)
x = \(\dfrac{57}{40}\)
b, 7 - x =\(\dfrac{5}{12}\)
x = 7 - \(\dfrac{5}{12}\)
x = \(\dfrac{79}{12}\)
câu d : ( x - 2 ) . ( x + 4 ) = 0
=) x - 2 =0 hay x + 4 = 0
x = 0 + 2
x = 2
x = 0 - 4
x = - 4
Vậy x = 2 ; x = -4
a)x=4
b)nhiều lắm
c)x không thoả mãn
d)x=2 hoặc x=-4