a) 9 - 25 = (7 - x) - (25 + 7) $\Rightarrow$ 9 - 25 = 7 - x - 25 - 7 $\Rightarrow$ x = -9;                             

b) -6x = 18 $\Rightarrow$ x = -3;

c) 35 - 3.|x| = 5. (2$^{3}$ - 4) $\Rightarrow$ 35 - 3.|x| = 20 $\Rightarrow$ 3.|x| = 15  $\Rightarrow$ |x| = 5  $\Rightarrow$ x = 5 hoặc x = -5;

d) 10 + 2.|x| = 2. (3$^{2}$ - 1) $\Rightarrow$10 + 2.|x| = 16 $\Rightarrow$ 2.|x| = 6 $\Rightarrow$ |x| = 3 $\Rightarrow$ x = 3 hoặc x = -3.