The Arsacid Dynasty ruled Parthia, which included the Iranian plateau and intermittently Mesopotamia, from 253 BC until their overthrow by the Sassanid Dynasty in AD 224. The members of this dynasty include:
... characteristic 2, the element 2a is zero and it is impossible to divide by it.)
The symbol
<math>\pm \sqrt {b^2-4ac}</math>
in the formula should b ...