题目

Each October 15, over 200 million people around the world take part in Global Handwashing Day.Research shows that not enough people wash their hands with soap. Experts believe that this leads to the deaths of millions of people every year.Myriam Sidibe says that soap is “the most beautiful invention in public health”. He knows that washing hands with soap can have a big influence on reducing flu(流感) and other diseases. It can also prevent babies from getting sick and keep children healthy.However, washing hands with soap doesn't appear as fast as you might think. This may happen in poo若最简二次根式与是同类二次根式，则a=    ．