7/5;7/6 và 3/2

1 + 1 = 2

2 + 2 = 4 

3 + 3 = 6

4 + 4 = 8

5 + 5 = 10

ĐỔI TK NHA

2

4

6

8

10

Mk sẽ giúg

\(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{\left(2x+1\right).\left(2x+3\right)}=\frac{15}{93}\)

\(2.\left(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{\left(2x+1\right).\left(2x+3\right)}\right)=2.\frac{15}{93}\)

\(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{\left(2x+1\right).\left(2x+3\right)}=\frac{30}{93}\)

\(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{2x+1}-\frac{1}{2x+3}=\frac{10}{31}\)

\(\frac{1}{3}-\frac{1}{2x+3}=\frac{10}{31}\)

\(\frac{1}{2x+3}=\frac{1}{3}-\frac{10}{31}\)

\(\frac{1}{2x+3}=\frac{1}{93}\)

=> 2x + 3 = 93

=> 2x = 93 - 3

=> 2x = 90

=> x = 90 : 2

=> x = 45

Vậy x = 45

sai rồi

4/5+1/5:2/5

=4/5+1/5x5/2

=4/5+1/2

=8/10+5/10

=13/10

4/5 + 1/5 : 2/5 = 4/5 + 1/5 x 5/2 = 4/5 + 1/2 = 8/10 + 5/10 = 13/10

`@` `\text {Ans}`

`\downarrow`

`1/3+6/9+4/5+5/25`

`= 1/3+2/3+4/5+1/5`

`= 1+1`

`= 2`

`4/7*2/5+4/7*3/5-1/7`

`= 4/7*(2/5+3/5)-1/7`

`= 4/7*1-1/7`

`= 4/7-1/7=3/7`

.....................................................

\(\left(x+\dfrac{1}{5}\right)^2=\dfrac{9}{25}\)

\(\left(x+\dfrac{1}{5}\right)^2=\left(\dfrac{3}{5}\right)^2\)

➩ \(x+\dfrac{1}{5}=\dfrac{3}{5}\)

    \(x=\dfrac{3}{5}-\dfrac{1}{5}\)

   \(x=\dfrac{2}{5}\)

thank bạn

1: \(\left(x-3\right)\left(2x-5\right)-3x\left(x+4\right)\)

\(=2x^2-5x-6x+15-3x^2-12x\)

\(=-x^2-23x+15\)

2: \(\left(\dfrac{1}{2}x+5\right)\left(2x-\dfrac{1}{5}\right)\)

\(=x^2-\dfrac{1}{10}x+10x-1\)

\(=x^2+\dfrac{99}{10}x-1\)