a) x2 - 4x = 0
<=> x(x - 4) = 0
<=> x = 0 hoặc x - 4 = 0
<=> x = 0 hoặc x = 4
b) 4x - (3 + 5x) = 14
<=> 4x - 3 - 5x = 14
<=> - x = 14 +3
<=> - x = 17
=> x = - 17
c)\(\frac{-7^5.3^3}{7^2.\left(-3\right)^3}=\frac{-7^5.3^3}{-7^2.3^3}=\frac{7^5}{7^2}=7^3=343\)