đổi k ko,mk hứa sẽ k lại(nếu ko làm chó!!!!!!!!!!!!!)

Bài 1: <Cho là câu a đi>:

a. \(\frac{1}{2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x\left(x+1\right)}=\frac{49}{50}\) 

\(\rightarrow\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x\left(x+1\right)}=\frac{49}{50}\) 

\(\rightarrow1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{49}{50}\) 

\(\rightarrow1-\frac{1}{x+1}=\frac{49}{50}\) 

\(\rightarrow\frac{1}{x+1}=1-\frac{49}{50}=\frac{1}{50}\) 

\(\rightarrow x+1=50\rightarrow x=49\) 

Vậy x = 49.

a) \(\frac{-2}{5}+\frac{5}{6}.x=\frac{-4}{15}\)

\(\frac{5}{6}.x=\frac{-4}{15}-\frac{-2}{5}\)

\(\frac{5}{6}.x=\frac{2}{15}\)

\(x=\frac{2}{15}:\frac{5}{6}\)

\(x=\frac{4}{25}\)

b) \(\left(x-\frac{1}{5}\right)\left(y+\frac{1}{2}\right)\left(z-3\right)=0\)

\(x-\frac{1}{5}=0\)

\(x=0+\frac{1}{5}\)

\(x=\frac{1}{5}\)

ko biết thi lam sao ma noi

chiu nha hahaha

Câu a:

- \(\frac12\)(3 - 2\(x\)) - 7 = 5 - \(\frac13\)(\(x\) - \(\frac45\))

- \(\frac32\) + \(x\) - 7 = 5 - \(\frac13x\) + \(\frac{4}{15}\)

\(x\) + \(\frac13x\) = 5 + \(\frac{4}{15}\) + 7 + \(\frac32\)

(1 + \(\frac13\))\(x\) = \(\frac{150}{30}\) + \(\frac{8}{30}\) + \(\frac{210}{30}\) + \(\frac{45}{30}\)

\(\frac43x\) = \(\frac{158}{30}\) + \(\frac{210}{30}\) + \(\frac{45}{30}\)

\(\frac43x\) = \(\frac{368}{30}\) + \(\frac{45}{30}\)

\(\frac43x\) = \(\frac{413}{30}\)

\(x\) = \(\frac{413}{30}\) : \(\frac43\)

\(x\) = \(\frac{413}{40}\)

Vậy \(x=\frac{413}{40}\)

Câu b:

(5 - 3x/2) : - 1 3/8 = - 7 1/3

(5 - 3x/2) : (-11/8) = - 22/3

5 - 3x/2 = - 22/3 x (-11/8)

5 - 3x/2 = 121/12

3x/2 = 5 - 121/12

3x/2 = - 61/12

x = - 61/12 : 3/2

x = -61/18

Vậy x = - 61/18

Ta có : 

\(\frac{-x}{3}=\frac{27}{4}\) \(\Rightarrow\) \(x=\frac{-81}{4}\)

\(\frac{3}{y^2}=\frac{27}{4}\) \(\Rightarrow\) \(y=\sqrt{\frac{4}{9}}=\frac{2}{3}\)

\(\frac{\left(z+3\right)^3}{-4}=\frac{27}{4}\) \(\Rightarrow\) \(z=-3\)

\(\frac{\left|t\right|-2}{8}=\frac{27}{4}\) \(\Rightarrow\) \(\orbr{\begin{cases}t=56\\t=-56\end{cases}}\)

Vậy ... 

Cảm ơn Phùng MInh Quân nha!!!

Câu a:

- 2/3.(x -1/4) = 1/3.(2x + 1)

- 2/3x + 1/6 = 2/3x + 1/3

2/3x + 2/3x = 1/6 - 1/3

4/3x = 1/6 - 2/6

4/3x = - 1/6

x = -1/6 : 4/3

x = -1/8

Vậy x = - 1/8

Câu c:

(x -y^2 + z)^2 + (y - 2)^2 + (z + 3)^2 = 0 (1)

Vì : (x - y^2 + z)^2 ≥ 0 ∀ x; y; (y - 2)^2 ≥ 0 ∀ x; (z + 3)^2 ≥ 0 ∀ z

Nên (1) xảy ra khi cà chỉ khi:

x - y^2 + z = 0 (1) ; y - 2 = 0 và z + 3 = 0

y - 2 = 0

y =2

z + 3 = 0

z =- 3

Thay y = 2; z = - 3 vào (1) ta có:

x - 4 - 3 = 0

x = 4 + 3

x = 7

Vậy (x; y; z) = (7; 2; -3)