why do we need to put negative sign in the "kt" (example dx/dt= -kt) in the application of differential equations in the decomposition of radioactive substances?

Question

shubhamsrg · Answer

because its decreasing,,and not increasing
for eg. if you say rate is inc by 2,,its different in notation than decreasing by 2
dx/dt =2 <--inc
3x/dt=-2 <-- dec

anonymous · Answer

because it is stupid
$k$ is a variable and so of course can be positive or negative