Christoff Rudolff was a German mathematician who was the first to use the radical symbol (√) in his book Behend und hübsch Rechnung durch die kunstreichen regeln Algebre so gemeincklich die Coss genent werden (Agile and Fair Calculation by the Ars Magna of Algebraic Rules, otherwise known as The Coss) printed in Strasburg in 1525. He created the modern radical sign without the upper bar (vinculum). The mathematician René Descartes added the horizontal bar to Christoff’s symbol in his book La Géométrie, published in 1637. Christoff Rudolff (1499-1545)