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5

You can do something like this: Simplify[Sqrt[x^2]] (* Sqrt[x^2] *) $Assumptions = _ ∈ Reals (* _ ∈ Reals *) Simplify[Sqrt[x^2]] (* Abs[x] *) This tells those functions that have an Assumptions option that any expression is considered real. Caveat: This refers to any expression, not just any variable! So you get this now: Simplify[Sqrt[x] ∈ Reals] (* ...


0

Clear[s]; eqns = {s'[t] == l t, s[0] == 0}; The solution does not vary with a Table[DSolve[eqns, s, {t, 0, a}][[1]], {a, Range[5, 50, 5]}] // Union (* {{s -> Function[{t}, (l t^2)/2]}} *) So just use soln = DSolve[eqns, s, t][[1]] (* {s -> Function[{t}, (l t^2)/2]} *) eqns /. soln (* {True, True} *) Consequently, s[t_] = l t^2/2;



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