Before looking at his remarkable contribution to complex numbers we should remark that Bombelli first wrote down how to calculate with negative numbers. He wrote (see or):
Bago naghahanap sa kanyang kapuna-puna na kontribusyon sa mga komplikadong mga numero namin ay dapat na pangungusap na Bombelli unang wrote down kung paano kinakalkula na may negatibong numero. He wrote (makita o):