a) x - (-7) = -8 + (-2)

x + 7 = -8 - 2

x + 7 = -10

x = -10 - 7

x = -17

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

x + (-3) = 3 - 7

x - 3 = -4

x = -4 + 3

x = -1

c) (12 - x) - (-10) = -25

(12 - x) + 10 = -25

12 - x = -25 - 10

12 - x = -35

x = 12 - (-35)

x = 12 + 35 = 47

d) (-20) - (15 - x) = -50

15 - x = -20 - (-50)

15 - x = -20 + 50

15 - x = -30

x = 15 - (-30)

x = 15 + 30

x = 45

\(\Rightarrow\orbr{\begin{cases}x-\frac{1}{2}=0\\1+5x=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{1}{2}\\5x=-1\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{1}{2}\\x=-\frac{1}{5}\end{cases}}\)

\(\left(x-\frac{1}{2}\right)\left(1-5x\right)=0\)
 

=>\(\left(x-\frac{1}{2}\right)=0\)hoặc\(1-5x=0\)

* \(x-\frac{1}{2}=0\Rightarrow x=\frac{1}{2}\)

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

Vậy x = 1/2 hoặc x = -1/5

(x - 2)² - (x + 3)² - 4(x + 1) = 5

<=> x² - 4x + 4 - x² - 6x - 9 - 4x - 4 = 5

<=> -14x - 9 = 5

<=> -14x = 5 + 9

<=> -14x = 14

<=> x = -1

=> x = -1

Ta có: \(\frac{a}{b}\frac{b}{c}=\frac{b}{c}\)

\(\Rightarrow\frac{10}{a+b}+10b+c=\frac{b}{c}\)

Áp dụng tính chất dãy số bằng nhau ta có:

\(10a+\frac{b}{10b+c}=\frac{b}{c}=10a+b-\frac{b}{10b+c-c}=\frac{10a}{10b}=\frac{a}{b}\)

\(\frac{\Rightarrow b}{c}=\frac{a}{b}\Rightarrow ac=b^2\)

đpcm.