To prove the equivalence, we expand Expression one:
\[ (x - 5)(x + 3) = x^2 + 3x - 5x - 15 = x^2 - 2x - 15. \]
Next, simplify Expression two:
\[ 2x^2 - x^2 - 2x - 20 + 5 = x^2 - 2x - 15. \]
Since both expressions simplify to \(x^2 - 2x - 15\), they are equivalent; hence, the result shows that both expressions represent the same quadratic function.