Respuesta :

Answer:

dz/dt = -(3x + 9y)/z

Step-by-step explanation:

x² + y² + z² = 9

2x dx/dt + 2y dy/dt + 2z dz/dt = 0

x dx/dt + y dy/dt + z dz/dt = 0

x * 3 + y * 9 + z dz/dt = 0

so

dz/dt = -(3x + 9y)/z