c, (2\(\times\) \(x\) - 3) \(\times\) 5 = 4

    2 \(\times\) \(x\) - 3       = \(\dfrac{4}{5}\)

     2 \(\times\) \(x\)            = 0,8 + 3

      2\(x\)                = 3,8

        \(x\)                 = \(3,8\) : 2

        \(x\)                 = 1,9 

d, 1 + 3 + 5 +....+\(x\)   = 36

    (\(x\) + 1)\(\times\) \(x\): 2      = 36

     (\(x+1\)) \(\times\)\(x\)         = 72 

     (\(x+1\))\(\times\)\(x\)           = 8 x 9

      \(x\)                         = 8

a) (X - 5) x 4 = 36

⇒         X - 5 = 36 : 4

⇒         X - 5 = 9

⇒              X = 9 + 5

⇒              X = 14

     Vậy X = 14 

b) (48 - X) x 2 = 14

⇒         48 - X = 14 : 2

⇒         48 - X = 7

⇒                X = 48 - 7

⇒                X = 41

    Vậy X = 41

\(B=\frac{36}{1.3.5}+\frac{36}{3.5.7}+\frac{36}{5.7.9}+...+\frac{36}{25.27.29}\)

   \(=9.\left(\frac{4}{1.3.5}+\frac{4}{3.5.7}+\frac{4}{5.7.9}+...+\frac{4}{25.27.29}\right)\)

    \(=9.\left(\frac{1}{1.3}-\frac{1}{3.5}+\frac{1}{3.5}-\frac{1}{5.7}+\frac{1}{5.7}-\frac{1}{7.9}+...+\frac{1}{25.27}-\frac{1}{27.29}\right)\)

    \(=9.\left(\frac{1}{3}-\frac{1}{675}\right)\)

    \(=9.\frac{224}{675}\)

    \(=\frac{224}{75}\)

THIẾU

\(=\frac{224}{75}< \frac{225}{75}=3\)

Vậy \(B< 3\)

mấy bọn nguuuuuuuuuuuuuuuuuu

5.x - 9 = 5 + 3.x

5x - 3x = 5 + 9

2x = 14

x = 14 : 2

x = 7

--------------------

(5x + 1)² = 36/49

5x + 1 = 6/7 hoặc 5x + 1 = -6/7

*) 5x + 1 = 6/7

5x = 6/7 - 1

5x = -1/7

x = -1/7 : 5

x = -1/35

*) 5x + 1 = -6/7

5x = -6/7 - 1

5x = -13/7

x = -13/7 : 5

x = -13/35

Vậy x = -13/35; x = -1/35

--------------------

2ˣ⁻¹ = 16

2ˣ⁻¹ = 2⁴

x - 1 = 4

x = 4 + 1

x = 5

\(a,96-3\left(x+8\right)=42\\ \Rightarrow3\left(x+8\right)=54\\ \Rightarrow x+8=18\\ \Rightarrow x=10.\\ b,15.5\left(x-25\right)-225=0\\ \Rightarrow75\left(x-25\right)-225=0\\ \Rightarrow75\left(x-25\right)=225\\ \Rightarrow x-25=3\\ \Rightarrow x=28.\\ c,250:x+15=25\\ \Rightarrow250:x=10\\ \Rightarrow x=25\\ d,36:\left(x-5\right)=2^2\\ \Rightarrow36:\left(x-5\right)=4\\ \Rightarrow x-5=9\\ \Rightarrow x=14.\\ e,\left[3.\left(70-x\right)+5\right]:2=46\\ \Rightarrow3.\left(70-x\right)+5=92\\ \Rightarrow3\left(70-x\right)=87\\ \Rightarrow70-x=29\\ \Rightarrow x=41.\)

a, \(\frac{2}{x}=\frac{y}{4}\Leftrightarrow xy=8\)

Suy ra : \(x;y\inƯ\left(8\right)=\left\{1;2;4;8\right\}\)tự lập bảng 

b, Xét : \(\frac{1}{x}=\frac{5}{15}\Leftrightarrow\frac{5}{5x}=\frac{5}{15}\Leftrightarrow x=3\)

\(\frac{y}{21}=\frac{5}{15}\Leftrightarrow15y=105\Leftrightarrow y=3\)

\(\frac{10}{z}=\frac{5}{15}\Leftrightarrow5z=150\Leftrightarrow z=30\)

c, tương tự b 

1) \(\left(5+x\right)^2-36=0\)

\(\Rightarrow\left(5+x-6\right)\left(5+x+6\right)=0\Rightarrow\left(x-1\right)\left(x+11\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=1\\x=-11\end{matrix}\right.\)

2) \(\Rightarrow\left(7x-11\right)^3=1000=10^3\)

\(\Rightarrow7x-11=10\Rightarrow7x=21\Rightarrow x=3\)

Đ

Đ

S

3/5 giờ = 36 phút  Đ

2/3 x 4/5 x 3/2= 4/5   Đ

132/11 = 12 Đ

Đ

Đ

S

174 x 36 - 174 x 26
= 174 x ( 36 - 26 )
= 174 x 10
= 1740

2/3 x 4/5 + 1/8 x 2/3
= 2/3 x ( 4/5 + 1/8 )
= 2/3 x 37/40
= 37/60

`=174xx(36-26)`

`=174xx10=1740`

`=2/3xx(4/5+1/8)`

`=2/3xx37/40=37/60`

174 x ( 36-26) = 1740

\(\dfrac{2}{3}x\left(\dfrac{4}{5}+\dfrac{1}{8}\right)=\dfrac{2}{3}x\dfrac{37}{40}=\dfrac{37}{60}\)

a: Ta có: \(\left(x+2\right)^2+\left(2x-1\right)^2-\left(x-3\right)^2=36\)

\(\Leftrightarrow x^2+4x+4+4x^2-4x+1-x^2+6x-9=36\)

\(\Leftrightarrow4x^2+6x-4-36=0\)

\(\Leftrightarrow4x^2+6x-40=0\)

\(\text{Δ}=6^2-4\cdot4\cdot\left(-40\right)=676\)

Vì Δ>0 nên phương trình có hai nghiệm phân biệt là:

\(\left\{{}\begin{matrix}x_1=\dfrac{-6-26}{8}=-4\\x_2=\dfrac{-6+26}{8}=\dfrac{5}{2}\end{matrix}\right.\)

\(a)x=\dfrac{1}{4}+\dfrac{5}{13}=\dfrac{33}{52}.\\ b)\dfrac{x}{3}=\dfrac{2}{3}+\dfrac{-1}{7}.\\ \Leftrightarrow\dfrac{x}{3}=\dfrac{11}{21}.\\ \Leftrightarrow\dfrac{7x}{21}=\dfrac{11}{21}.\\ \Rightarrow7x=11.\\ \Leftrightarrow x=\dfrac{11}{7}.\\ c)\dfrac{x}{3}=\dfrac{16}{24}+\dfrac{24}{36}=\dfrac{2}{3}+\dfrac{2}{3}=\dfrac{4}{3}.\\ \Rightarrow x=4.\\ d)\dfrac{x}{15}=\dfrac{1}{5}+\dfrac{2}{3}=\dfrac{13}{15}.\\ \Rightarrow x=13.\)