By Paul Carsten BEIJING (Reuters) - The death of a student following experimental cancer treatment he found through China's biggest search engine, Baidu Inc , has exposed the faultlines in the company's business model, which relies heavily on income from the country's lightly regulated health sector. Before his death, student Wei Zexi, 21, criticized the military-run hospital that provided the failed treatment for misleading claims about its effectiveness and accused Baidu, which controls 80 percent of the Chinese search market, of promoting false medical information. This week the health ministry began an investigation into the hospital, while the internet regulator began an investigation into Baidu.