Error when integrating absolute value

[parisse]

I guess you mean int(k*abs(cos(x)),x,-pi/2,3*pi/2);
There is a warning displayed in the terminal. If you compute the integral without k, the calculator can check the discontinuities of the antiderivative, but not with k, the check is disabled because checking for more complex inputs could raise endless computations.
This input is simple, it's certainly possible to solve this case, but at some point you will find a similar error, whatever I code.