a )   A = 84 − x + 84 − 23 ;       A = 84 − x − 84 − 23       A = 84 − 84 − x − 23       A = − x − 23 b )   B = 39 + x − 15 − 39 ;       B = 39 + x − 15 − 39       B = 39 − 39 + x − 15       B = x − 15

11- (x+84) = 97 

=> 11 -x - 84 = 97 

=> 11-x = 181

=> x= 11- 181 

=> x= -170

cấc câu sau làm tương tự

11 - (x + 84) = 97

x + 84 = 11 - 97

x + 84 = -86

x = -86 - 84

x = -170

-(x + 84) + 213 = -16

-x - 84 = -16 - 213

-x - 84 = -229

-x = -229 + 84

-x = -145

x = 145

x + (-35) = 18

x - 35 = 18

x = 18 + 35

x = 53

-2x -(-17)= 15

-2x + 17 = 15

-2x = 15 - 17

-2x = -2

x = -2 : (-2)

x =1

a,11-(x+84)=97

11-x-84   =97

11-x         =97+84

11-x         =181

x              =11-181

x              =-170

b,-(x+84)+213=-16

-x-84+213   =-16

-x-84           =-16-213

-x-84           =-229

-x                 =-229+84

-x                 =-145

x                  =145

c,x+(-35)=18

x-35    =18

x         =18+35

x         =53

d,-2x-(-17)=15

-2x+17      =15

-2x            =15-17

-2x            =-2

-x              =-2:2

-x              =-1

x               =1

X × 15 = 84
X          = 84 : 15
X          = 5,6

X × 15 = 84
X          = 84 : 15
X          = 5,6

a, -(x+84) + 213=-16

-(x+84)+231=-16

-(x+84)=-16-231

-(x-84)=-247

=>x+84=247

x=247-84

x=163

b, -12 (x-15)+ 7(3-x) = 15

-12x+180+21-7x=15

(-12x-7x)+(180+21)=15

-19x+201=15

-19x=15-201

-19x=-186

x=-186:-19

x=186/19

a, x = 163

b, x = 186/19

k cho minh nha

Vì x chia hết cho 12, cho15 và cho 18 nên x là BC của 12, 15 và18.

B₍₁₂₎= 0;12;24;36;..................;144; 156; 168; 180;.........

B₍₁₅₎= 0;15;30;45;..................;135;150;165;180;...........

B₍₁₈₎= 0;18;36;54;..................;126;144;162;180;.............         

=> BC_(12;15;18)=0;180;.......

Vì 0<x<300 nên x = 180

Vậy x =180

\(\Leftrightarrow\dfrac{x+100}{86}+\dfrac{x+100}{85}+\dfrac{x+100}{84}+\dfrac{x+100}{83}=0\)

=>x+100=0

hay x=-100

\(=\frac{7}{12}.\frac{16}{21}.15+4=\frac{4}{9}.15+4=\frac{32}{3}\)

84 : ( 324 - 18 + 36 - x ) =  19 - 15 = 4

324 - 18 + 36 - x = 84 : 4 = 21

306 + 36 - x = 21

342 - x = 21

x = 342 - 21 = 321

Vậy x = 321