\(90-120\div x\times0,3=45\)

\(120\times\dfrac{1}{x}\times0,3=90-45\)

\(\dfrac{36}{x}=45\)

\(x=\dfrac{4}{5}\)

 

\(8765\div90=\dfrac{1753}{18}\)\(=97,4\)

\(1325\times65=86125\)

\(6543\div89=73,52\)

=>a x (0,5+0,3)=0,69

=>a x 0,8 = 0,69

=>a = 0,69/0,8

=>a=0,8625

a x 0,5 + a x 0,3 = 0,69

a x (0,5 + 0,3 )=0,69

a  x 0,8    =0,69

a              =0,69 :  0,8

a               =0,0850

a.<0,5+0,3>=0,69

a.0,8=0,69

   a=0,69:0,8

    a=0,8625

                                        dấu chấm là dấu nhân

\(\left(x-3\right)\left(x^2+3x+9\right)+x\left(x+2\right)\left(2-x\right)=1\)

\(x^3-3^3+x\left(2^2-x^2\right)=1\)

\(x^3-27+4x-x^3=1\)

\(4x-27=1\)

\(4x=28\)

\(x=7\)

Vậy x = 7

\(\left(x-3\right)\left(x^2+3x+9\right)+x\left(x+2\right)\left(2-x\right)=1\)

\(\Rightarrow x^3-3^3+x\left(2^2-x^2\right)=1\)

\(\Rightarrow x^3-27+4x-x^3=1\)

\(\Rightarrow4x-27=1\)

\(\Rightarrow4x=28\)

\(\Rightarrow x=7\)

Vậy \(x=7\)

\(\frac{\left(120+60\right)}{12}=\frac{120}{12}+\frac{60}{12}=10+5=15\)

\(78\cdot31+78\cdot17+78\cdot24+22\cdot72=78\left(31+17+24\right)+22\cdot72\)

\(=78\cdot72+22\cdot72=72\left(78+22\right)=72\cdot100=7200\)

\(997+86=997+\left(83+3\right)=\left(997+3\right)+83\)

\(=1000+83=1083\)

\(5\cdot25\cdot2\cdot37\cdot4=\left(5\cdot2\right)\cdot\left(25\cdot4\right)\cdot37\)

\(=10\cdot100\cdot37=37000\)

\(558+336+442+664=\left(558+442\right)+\left(336+664\right)\)

\(=1000+1000=2000\)

5 x 25 x 2 x 37 x 4

= ( 5 x 2 ) x ( 25 x 4 ) x 37

= 10 x 100 x 37

= 1000 x 37

= 37000

6/11.x = 9/2.y = 15/5.z 6/11.x = 9/2.y = 3.z =) 6/11.x = 9/2.(-3)=(-y).z =) 6/11.x = (-27/2) = (-y).z • x = (-27/2) : 6/11 x = -99/4 ( mk làm tắt) Vì x = (-99/4) =) 6/11.(-99/4)= 9/2.y= 3.z =) -27/2=9/2.y=3.z •9/2.y=-27/2 y=-27/2:9/2 y=-3 •3.z=-27/2 z=-27/2:3 z= -9/2 Vậy x=-99/4;y=-3;z=-9/2 (Mk làm bừa câu này còn câu còn lại ko biết)

( 123 x 148 + 8879 ) x ( 120 – 240 : 24 x 12)

= ( 123 x 148 + 8879 ) x  (  120 - 120)

= ( 123 x 148 + 8879 ) x 0 

= 0 

`( 123 xx 148 + 8879 ) xx ( 120 – 240 : 24 xx 12)`

`=> ( 18204 + 8879) xx  (  120 - 120)`

`=> ( 18204 + 8879) xx 0 `

`=> 0 `

(123 x 148 + 8879)x(120-240:24x12)

= (123x148+8879)x (120-120)

=27 083x 0 

= 0 

|x+5/4| = 0,3 + 4/5

|x+5/4| = 11/10

x+5/4 = 11/10  hoac    x+5/4 = -11/10

x= 11/10 - 5/4  hoac    x= -11/10 - 5/4

x= -3/20           hoac    x= -47/20