填空：
(1) 方程x2+2x+1=0的根x2=______， x2=______，x1+x2=_______，x1x2=_______；
(2) 方程x2-3x-1=0的根x1=______，x2=______，x1+x2=_______，x1x2=_______；
(3) 方程3x2+4x-7=0的根x1=______，x2=______，x1+x2=_______，x1x2=_______ ；
(4)由(1)(2)(3)你能得到什么猜想？你能证明你的猜想吗？
解：（1）x1=-1，x2=-1，x1+x2=-2，x1x2=1 ；
（2）x1=
，x2=
，x1+x2=3，x1x2=1；
（3）x1=-7/3，x2=1，x1+x2=-4/3，x1x2=-7/3；
（4）“略”。
Food is important. Everyone needs to well if he wants to have a strong body. Our minds also need a kind of food. This kind of food is . We begin to get knowledge even when we are young. Small children are in everything around them. They learn something while they and listening. When they are getting older they begin storybooks, science books and anything they like. When they find , they have to ask questions and try to get the answers. What is the best to get knowledge? If we learn by ourselves, we the most knowledge. If we are getting answers from and don’t ask why, we will never learn more or understand better.
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