Answer:
B
Step-by-step explanation:
We are given that x and y are functions of time t such that x and y is a constant. So, we can write the following equation:
[tex]x(t)+y(t)=k,\text{ where $k$ is some constant}[/tex]
The rate of change of x and the rate of change of y with respect to time t is simply dx/dt and dy/dt, respectively. So, we will differentiate both sides with respect to t:
[tex]\displaystyle \frac{d}{dt}\Big[x(t)+y(t)\Big]=\frac{d}{dt}[k][/tex]
Remember that the derivative of a constant is always 0. Therefore:
[tex]\displaystyle \frac{dx}{dt}+\frac{dy}{dt}=0[/tex]
And by subtracting dy/dt from both sides, we acquire:
[tex]\displaystyle \frac{dx}{dt}=-\frac{dy}{dt}[/tex]
Hence, our answer is B.
