SHOWTIME:TRUE$
LOADPRINT:FALSE$
EQN1:A*COS(P2)=S+B*COS(P3);
EQN2:A*SIN(P2)=E+B*SIN(P3);
/* Declare p2, p3 and s to be time-dependent. */
DEPENDS([P2,P3,S],T);
/* [1] From equations 1 and 2, eliminate P3: */
EQN3:EXPAND((EQN1-S)^2+(EQN2-E)^2);
EQN3:TRIGSIMP(EQN3);
/* [2] Using the results of step 1, solve for S in terms of
       a,b,e,p2: */
S_SOLUTION:SOLVE(EQN3,S);
/* Note that this differs from the result given.
   [3] Take the derivative of eqn2 wrt t:  */
EQN3:DIFF(EQN2,T);
/* [4] Solve for p3-dot in terms of a, b, p2, p2-dot,p3. */
P3_DOT:SOLVE(%,DIFF(P3,T));
/* [5] Take the derivative of eqn2 wrt t:  */
EQN5:DIFF(EQN1,T);
/* [6] Solve for s-dot in terms of a, b, p2, p2-dot,p3. */
SOLVE(EQN5,DIFF(s,T));
%,P3_DOT,FACTOR;
TRIGREDUCE(%);
/* [7] */
Z:I*(A*COS(P2)/(B*COS(P3)))^2;
DIFF(Z,P2);