Question

Tìm \(x,y,z\)biết : \(\frac{x}{7}=\frac{-y}{4}=-\frac{8}{z}=\frac{-28}{49}\)

Answer 1

\(\frac{x}{7}=\frac{-y}{4}=\frac{-8}{z}=\frac{-28}{49}\)

Cái này thì phải làm ngược từ phải sang trái =))

* \(\frac{-8}{z}=\frac{-28}{49}\Leftrightarrow-28z=-8\cdot49\Leftrightarrow-28z=-392\Leftrightarrow z=14\)

* \(\frac{-y}{4}=\frac{-8}{14}\Leftrightarrow-14y=-8\cdot4\Leftrightarrow-14y=-32\Leftrightarrow y=\frac{16}{7}\)

* \(\frac{x}{7}=\frac{-\frac{16}{7}}{4}\Leftrightarrow4x=-\frac{16}{7}\cdot7\Leftrightarrow4x=-16\Leftrightarrow x=-4\)

Answer 2

\(\frac{x}{7}=\frac{-y}{4}=\frac{-8}{z}=\frac{-28}{49}\)

\(\Rightarrow\frac{x}{7}=\frac{-28}{49};\frac{-y}{4}=\frac{-28}{49};\frac{-8}{z}=\frac{-28}{49}\)

+)\(\frac{x}{7}=\frac{-28}{49}\Rightarrow49x=\left(-28\right).7\Rightarrow49x=-196\Rightarrow x=\frac{-196}{49}=-4\)

+)\(\frac{-y}{4}=\frac{-28}{49}\Rightarrow-49y=\left(-28\right).4\Rightarrow-49y=-112\Rightarrow y=\frac{-112}{49}\)

+)\(\frac{-8}{z}=\frac{-28}{49}\Rightarrow-28z=49.\left(-8\right)\Rightarrow-28z=-392\Rightarrow z=\frac{-392}{-28}=14\)

Vậy x=-4;y=\(\frac{-112}{49}\);z=14

Chúc bạn học tốt