（8分）如图，E、F是□ABCD对角线
上的两点，且
.
求证：（1）
；
（2）
.
（8分）如图，E、F是□ABCD对角线上的两点，且.
求证：（1）；
（2）.
证明：（1）
四边形
是平行四边形，
.
.······································································································ 2分
，
.
.······································································································ 3分
··························································································· 4分
(2)由
得
.，···························································································· 5分
四边形
是平行四边形. ··················································································· 7分
. 8分
解析:略