1次= \colorblue a + \colorred b                                                                                                                       
2次= \colorblue a  · \colorblue a + \colorblue a  · \colorred b + \colorred b  · \colorred b                                                          
3次= \colorblue a  · \colorblue a  · \colorblue a + \colorblue a  · \colorblue a  · \colorred b + \colorblue a  · \colorred b  · \colorred b + \colorr
                                                                                           
                                                                                           
                                                         ed b  · \colorred b  · \colorred b