The mathematician Girolamo Cardano is credited with the
Chapter 10, Problem 10.1.953(choose chapter or problem)
The mathematician Girolamo Cardano is credited with the first use (in 1545) of negative square roots in solving the now-famous problem, Find two numbers whose sum is 10 and whose product is 40. Show that the complex numbers 5 i15 and 5 i15 satisfy the conditions of the problem. (Cardano did not use the symbolism i15 or even 15. He wrote R.m 15 for 15, meaning radix minus 15. He regarded the numbers 5 R.m 15 and 5 R.m 15 as fictitious or ghost numbers, and considered the problem manifestly impossible. But in a mathematically adventurous spirit, he exclaimed, Nevertheless, we will operate.)
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