1.Tìm X:

a)  `x : 8 = 107,8 - 29,25`

`x:8=78,55`

`x=78,55xx8`

`x=628,4`

b) `x + 16,7 = 50,5 : 2,5`

`x+16,7=20,2`

`x=20,2-16,7`

`x=3,5`

2.Tìm X:

a) `x - 2,35  =  3,6 : 4,5` 

`x-2,35=0,8`

`x=0,8+2,35`

`x=3,15`

b) `189,5 - x = 7,2 xx 14`

`189,5 - x = 100,8`

`x=189,5-100,8`

`x=88,7`

3. Tính giá trị biểu thức :

`13,5 : 4,5 xx 2,4 + (156,9 – 80,6) `

`=3xx2,4+76,3`

`=7,2+76,3`

`=83,5`

4. Tính giá trị biểu thức :

`1,25 xx 4,2 + 119,6 : 5,2 – 23,19`

`=5,25+23-23,19`

`=5,06`

5. Tính giá trị biểu thức :

`14,75 – 7,15 : 5 + 2,6 xx 3,5`

`=14,75 – 1,43 + 9,1`

`=22,42`

6. Tính nhanh

a) `3,6 xx 78 + 78 xx 6,4=78xx(3,6+6,4)=78xx10=780`

b) `80 xx 5,29 xx 1,25=(80xx1,25)xx5,29=100xx5,29=529`

\(\Leftrightarrow2x+1+2x+2+2x+3+....+2x+101=5757\)

\(\Leftrightarrow2x.101+\left[1+2+3+....+101\right]=5757\)

\(\Leftrightarrow202x+\frac{\left[101+1\right]101}{2}=5757\)

\(\Leftrightarrow202x+5151=5757\)

\(\Leftrightarrow202x=606\)

\(\Leftrightarrow x=3\)

Vậy x=3

a: 5x=9,5

nên x=1,9

b: 42x=15,12

nên x=15,12:42=0,36

a, \(x=\dfrac{9,5}{5}=\dfrac{19}{10}\)

b, \(x=\dfrac{15,12}{42}=\dfrac{9}{25}\)

a.\(x\times5=9,5\)

\(\Rightarrow x=9,5:5=1,9\)

b.\(42\times x=15,12\)

\(\Rightarrow x=15,12:42=0,36\)

a) x * 2 + x * 3 = 60

x * ( 2 + 3 ) = 60

x = 60 : 5

x = 12

b) x * 15 - x * 9 = 78

x * ( 15 - 9 ) = 78

x = 78 : 6

x = 13

\(a.\)

\(\left(x-19\right)\left(x+21\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-19=0\\x+21=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=19\\x=-21\end{matrix}\right.\)

\(S=\left\{19,-21\right\}\)

\(b.\)

\(\left(53-x\right)\left(41+x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}53-x=0\\41+x=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=53\\x=-41\end{matrix}\right.\)

\(S=\left\{53,-41\right\}\)

Tìm x:

a) (x-19).(x+21)=0

<=>\(\left\{{}\begin{matrix}x-19=0< =>x=19\\x+21=0< =>x=-21\end{matrix}\right.\)

Vậy pt trên có tập nghiệm là: S={19;-21}

b)(53-x).(41+x)=0

<=>\(\left\{{}\begin{matrix}53-x=0< =>x=53\\41+x=0< =>x=-41\end{matrix}\right.\)

Vậy pt trên có tập nghiệm là S={53;-41}

a) x là 19 hoặc -21

b) x là 53 hoặc-41

cho tớ tim nhá

a,6,52

b,4,05

Tìm x:

a.  x + 4,64 = 9,26 + 1,9 

x + 4,64 = 11,16

x = 11,16 - 4,64

x = 6,52

b.  16  x  x  = 64,8

x = 64,8 : 16

x = 4,05

a) x+4,64 = 11,16

    x          =11,16 - 4,64

    x          =    6,52

b) x         =64,8:16

    x         =  4,05

a) Ta có: \(\left|4-5x\right|=24\)

\(\Leftrightarrow\left[{}\begin{matrix}-5x+4=24\\-5x+4=-24\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}-5x=20\\-5x=-28\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-4\\x=\dfrac{28}{5}\end{matrix}\right.\)

Vậy: \(x\in\left\{-4;\dfrac{28}{5}\right\}\)

b) Ta có: \(\left(8+x\right)\left(6-x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x+8=0\\6-x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-8\\x=6\end{matrix}\right.\)

Vậy: \(x\in\left\{-8;6\right\}\)

a) \(\left|4-5x\right|=24\)

\(\Leftrightarrow\left[{}\begin{matrix}4-5x=24\\4-5x=-24\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-4\\x=\dfrac{28}{5}\end{matrix}\right.\)

b) \(\left(8+x\right)\left(6-x\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}8+x=0\\6-x=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-8\\x=6\end{matrix}\right.\)

a.|4-5.x|=24

TH1: 4-5.x=24

        ⇔5x=-20

        ⇔x=-4

TH1: 4-5.x=-24

        ⇔5x=28

        ⇔x=28/5

b.(8+x).(6-x)=0

\(\left\{{}\begin{matrix}8+x=0\\6-x=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=-8\\x=6\end{matrix}\right.\)

\(\text{a. 246 : x + 34 : x = 5 }\\ \left(246+34\right):x=5\\ \\280:x=5\\ x=280:5\\ x=56\)

\(\text{ b. 360 : x – 126 : x = 6}\\ \left(360-126\right):x=6\\ 234:x=6\\ x=234:6\\ x=39\)

\(a,246:x+34:x=5\\ \Rightarrow\left(246+34\right):x=5\\ \Rightarrow280:x=5\\ \Rightarrow x=56\\ b,360:x-126:x=6\\ \Rightarrow\left(360-126\right):x=6\\ \Rightarrow234:x=6\\ \Rightarrow x=39\)

`x+x xx2=1,02`

`=> x xx (1+2)=1,02`

`=> x xx 3=1,02`

`=> x=1,02:3`

`=> x=0,34`

`7,9-x+5,7=1,3`

`=>7,9-x=1,3-5,7`

`=>7,9-x=-4,4`

`=>x=7,9-(-4,4)`

`=>x=12,3`