Théodebald (French Thibaud or Théodebald , (d. 555) was the king of Austrasia from 547 or 548 to 555. He surrendered his country to his great-uncle Clotaire I.
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The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in the formula should be understood as "either of those element(s) of the field whose square equals b2 - ...