如图，在正方形ABCD中，E，F分别是边AD，DC上的点，且AF⊥BE.求证：AF＝BE
提示:1）Where did you go?
2）How did you go there?
3）Who did you go with?
4）How was the weather there?
5）What did you do there?
在某些恒星内部，3个α粒子结合成一个C核，C的质量是12.000000u， He的质量是4.001509u．（已知质量亏损1u相当于释放931.5Mev的能量）
He