Question

if..., the rate of change of y with respect to x=k, pi 13 years ago

Answer 1

\[y=\left| sinx \right|\], \[\pi<x< 2\pi\]

Answer 2

y=+-sinx
y'=+-cosx
saying that rate of change is constant, equal to k, means that secon derivative should be equal 0. So taking derivative one more time:
y''=-+sinx
it will be equal 0 at x=Pi and x=2Pi

Answer 3

but notice that your interval does not include the points x=Pi and x= 2Pi

Answer 4

or is it?
\[\pi\leq x\leq2\pi\]

Answer 5

it does not include those two values! thank you :)