a, \(\dfrac{x^2}{54}\) = \(\dfrac{-4}{x}\)

b, \(\dfrac{x}{2}\) = \(\dfrac{2y}{5}\) = \(\dfrac{4z}{7}\) và 3x+5y +7z=123

c \(\dfrac{x}{2}\) = \(\dfrac{2y}{3}\) = \(\dfrac{3z}{4}\) và x*y*z=-108

2. Tìm x:

A, \(\dfrac{5}{2}\)*x-\(\dfrac{1}{3}\)*X+2=\(\dfrac{3}{2}\) B, (2X-1)^2=\(\dfrac{1}{4}\)

C, ( X^2-16)*(4-5*X)=0 D, \(\dfrac{2\cdot X-1}{3}\)=\(\dfrac{X+2}{3}\)