`x/2 =y/3 =z/7 = (x+y-z)/(2+3-7)=(-12)/(-2)=6`

`x=6.2=12`

`y=6.3=18`

`z=6.7=42`

     `x xx45 - x xx28 + x=1098`

`=> x.(45-28+1) = 1098`

`=> x.18 = 1097`

`=> x = 1097 : 18`

`=> x = 1097/18`

Chọn `A) f(-1)=9`

$$\begin{gathered} (\mathrm{x}+6)\times (\mathrm{x}-4)=0 \\ \iff \left\{\begin{array}{l}\mathrm{x}+6=0\\ \mathrm{x}-4=0\end{array}\right. \\ \iff \left\{\begin{array}{l}\mathrm{x} = -6\\ \mathrm{x}=4\end{array}\right. \end{gathered}$$                        

Vậy `x=-6` hoặc `x=4`

`(96-16+47)-(48-16+96)`

`=127-128`

`=-1`

`12 dm^2 13cm^2 = 12,13 dm^2`

`100-7(x-5)=58`

`<=> 7(x-5)=42`

`<=> x-5 = 6`

`<=> x = 11`

`2^x-5=3^3`

`<=>2^x -5 = 27`

`<=> 2^x = 32`

`<=> 2^x =2^5`

`<=> x= 5`

`((-2)/5)^4 = 16/625`

`45:(x+2)=9`

`=>x+2=45:9`

`=> x+2 = 6`

`=> x = 6-2`

`=> x = 4`

`(-11) + (-22) + 32 - (-11)`

`=(-11)+(-22) + 32+11`

`=[(-11)+11] + [(-22)+32]`

`= 0 +10`

`=10`

`A = 57.13+13.63-13.20`

`A = 13.(57+63-20)`

`A = 1300`

`234,345 xx123 = 28824,435`

Cách `1`

`38:10+32:10 = (38+32):10=60:10=6`

Cách `2`

`38:10+32:10 = 38/10 + 32/10 = (38+32)/10=60/10=6`

`11-(-53+x)=97`

`<=>-53+x=-86`

`<=> x = -86 - (-53)`

`<=> x = -33`

`75 + (-75) = 0` (vì là hai số đối nhau)

`a,`

Ta thấy : 

`150` và `57` đều chia hết cho `3`

`=>` `150+57` chia hết cho `3`

`b,`

`12 xx (x-3)=144`

`<=> x-3 = 144:12`

`<=> x - 3=12`

`<=> x = 12+3`

`<=> x=15`

Vậy `x=15`

$$\begin{gathered} (x-3).(x+4)=0 \\ \iff \left\{\begin{array}{l}x-3=0\\ x+4=0\end{array}\right. \\ \iff \left\{\begin{array}{l}x=3\\ x=-4\end{array}\right. \end{gathered}$$               

Vậy `x=3` hoặc `x=-4`    

`67,33 = 67,3300`

`(-3/4)^2 = (-3/4) . (-3/4)=9/16`