20 12 the second question of the last question of the college entrance examination for mathematics in Shaanxi province, the first situation classified in the standard answer is not within the definition, is it necessary ~? It is necessary, because your purpose is to find out the maximum and minimum values of the function on [- 1, 1], and then find out their differences, so you should divide the symmetry axis into domain interval and domain interval, in which zero is discussed as the node, and outside it is about [- 1].