a) \(\dfrac{x}{-6}=\dfrac{-15}{45}\)

    \(\dfrac{-x}{6}=\dfrac{-15}{45}\)

    \(\dfrac{x}{6}=\dfrac{15}{45}\)

    \(x=\dfrac{\left(15\cdot6\right)}{45}\)

    \(x=2\)

b) \(\dfrac{x}{5}=\dfrac{16}{25}\)

    \(x=\dfrac{\left(16\cdot5\right)}{25}\)

    \(x=\dfrac{80}{25}\)

   \(x=\dfrac{16}{5}\)

c) \(\dfrac{5}{x-3}=\dfrac{20}{-12}\)

  \(x-3=\dfrac{\left(5\cdot-12\right)}{20}\)

 \(x-3=-3\)

 \(x=\left(-3\right)+3\)

\(x=0\)

d) \(\dfrac{2}{5}\cdot x=\dfrac{6}{35}\)

         \(x=\dfrac{6}{35}\div\dfrac{2}{5}\)

        \(x=\dfrac{3}{7}\)

86-84+82-80+...+8-6+4-2

=2+2+2+...+2+2+2 (có tất cả 21 số 2)

=2.21

=42

77-75+73-71+...+7-5+3-1

= 2 + 2 + ... + 2 ( có 38 số 2)

= 2 . 38

= 76

 tick đúng cho mình nhé !

a)(9x+2)x3=60

        9x+2 =60:3

        9x+2  =20

              9x =20-2

              9x=18

                x=18:9

                 x=2

a,x=2

b,x=2

c,x=9

o phan a 

(9x+2)*3=60

9x+2=20

9x=18

x=2

o phan b

71+(26-3x)/5=75

(26-3x)/5=75-71=4

26-3x=4*5=20

3x=26-20=6

x=6/3=2

vay x=2

o phan c 

(x-6)^2=9

(x-6)^2=3^2

=>x-6=3

=>x=9

vay x =9

ở phần d 

1+3+.....+x=465

=>(x+1)*(x-1)/2+(x+1)=465

=>(x+1)*(x-1)/2

a) 71 + \(\frac{26-3x}{5}=75\)

↔ \(\frac{26-3x}{5}=4\)

↔\(26-3x=20\)

↔x=2

b) \(x-17=\left(-8\right)-17\)

↔ \(x-17=-25\)

↔\(x=-8\)

c)\(\left(5x-2\right).6^3=3.6^5\)

↔\(\left(5x-2\right)=3.6^2\)

↔\(5x=110\)

↔\(x=22\)

d)\(\left(3x-2^4\right).7^3=2.7^4\)

↔\(3x-16=14\)

↔x=10

tick nha~~

(20-3.x):5=55-51

(20-3.x):5=4

20-3.x=4.5

20-3.x=20

3.x=20-20

3.x=0

x=0:3

x=0

không đc đừng ném mik nha