private void button3_Click(object sender, RoutedEventArgs e)
        {
            // 과제 등록 게시판으로 가기
            education_board_write edu_bo_wr = new education_board_write();

            Main.pageNavigation.PushBack(this);
            Main.pageNavigation.preClear();
            Main.pageFade.ShowPage(edu_bo_wr);
        }
 private void button3_Click(object sender, RoutedEventArgs e)
 {
     // 과제 등록 게시판으로 가기
     education_board_write edu_bo_wr = new education_board_write();
     Main.pageNavigation.PushBack(this);
     Main.pageNavigation.preClear();
     Main.pageFade.ShowPage(edu_bo_wr);
 }