How can I generate a sequence of random numbers Xi and Yi in [-1,1] ?

I am trying to simplify the last expression, it has assumptions in it. The numerator is a negative of the denominator so I am trying to get 1, Please help.

Could someone pleease clarify this error message below.

sol1 := dsolve({syst, theta1(0) = (1/2)*Pi, theta2(0) = (1/4)*Pi, (D(theta1))(0) = 0, (D(theta2)(0) = 0}, theta1(t), theta2(t), type = numeric, output = listprocedure);
Error, (in dsolve/numeric/process_input) system must be entered as a set/list of expressions/equations