Question

Cho x, y, z TLT  với 2, 3, 7 và 5x + y - 2z = 4. Tính x - 3y + 4z

Answer 1

Ta có : \(\frac{x}{2}=\frac{y}{3}=\frac{z}{7}\)

=> \(\frac{5x}{10}=\frac{y}{3}=\frac{2z}{14}=\frac{5x+y-2z}{10+3-14}=\frac{4}{-1}=-4\)

=> 5x = -40 => x = -8

;     y = -12

; 2x = -56 => z = -28

Do đó x - 3y + 4z = -8 - 3.(-12) + 4.(-28) = -8 - (-36) + (-112) = -84

Answer 2

Ta có: \(\frac{x}{2}=\frac{y}{3}=\frac{z}{7}\)

\(\Rightarrow\frac{5x}{10}=\frac{y}{3}=\frac{2z}{14}=\frac{5x+y-2z}{10+3-14}=\frac{4}{-1}=-4\)

\(\Rightarrow x=-4.2=-8\)

\(y=-4.3=-12\)

\(z=-4.7=-28\)

\(\Rightarrow x-3y+4z=-8-3.\left(-12\right)+4.\left(-28\right)=-84\)