[ww-bugs] Bug 4419: New: Error in the solution formulas for problem METU-NCC/Diff_Eq/laplace-step_exp_trig.pg

[bugzilla-daemon at webwork.maa.org]

http://bugs.webwork.maa.org/show_bug.cgi?id=4419

           Summary: Error in the solution formulas for problem
                    METU-NCC/Diff_Eq/laplace-step_exp_trig.pg
           Product: Problem Libraries
           Version: unspecified
          Platform: PC
               URL: /opt/webwork/courses/Math3503_2020W/templates/Library/
                    METU-NCC/Diff_Eq/laplace-step_exp_trig.pg_with_problem
                    Seed=1234
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Library (OPL)
        AssignedTo: gjennings at csudh.edu
        ReportedBy: slanery at unb.ca
        Web browser ---
           version:


There seems to be an error in the solution formulas in the case of a
denominator = 2 for the step function shift. It should be:

l71:     Formula($f_t,"(-1)^(($num+1)/2) sin(pi t)")->reduce ;
l74:     Formula($F_s,"(-1)^(($num+1)/2) pi / (s^2 + pi^2)")->reduce;

(rather than $num-1) for the cos case, and

l79:      Formula($f_t,"(-1)^(($num-1)/2) cos(pi t)")->reduce ;
l82:     Formula($F_s,"(-1)^(($num-1)/2) s / (s^2 + pi^2)")->reduce;

(rather than $num+1) for the sin case.

For we have:

cos(pi [t+$num/2]) = -sin(pi [t+($num-1)/2]) = -(-1)^{($num-1)/2} sin(pi t) =
(-1)^{($num+1)/2} sin(pi t)

sin(pi [t+$num/2]) = +cos(pi [t+($num-1)/2]) = (-1)^{($num-1)/2} cos(pi t)

-- 
Configure bugmail: http://bugs.webwork.maa.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are watching all bug changes.