整体思想是中学数学解题的重要方法之一，贯穿于数学学习的全过程．对于问题1，王老师给出了如下的提示：连接PA，利用△PAD与△PAB面积之和是菱形面积的$rac{1}{2}$，可求出PE+PF的值．（1）如图1，在菱形ABCD中，对角线AC，BD的长分别为6和8，点P为对角线BD上一动点（不与点B，D重合），过点P分别作AD和AB的垂线，垂足为点E和F，求PE+PF的值；（2）如图2，若ABCD为矩形，点M，N分别在边AD，BC上，将矩形ABCD沿直线MN折叠，使点D恰好与点B重合，点C落在点C′处．点P为线段MN上一动点（不与点M，N重合），过点P分别作直线BM，BC的垂线，垂足分别为E和F，以PE，PF为邻边作平行四边形PEGF，若DM=13，CN=5，求平行四边形PEGF的周长；（3）如图3，当点P是等边△ABC外一点时，过点P分别作直线AB，AC，BC的垂线，垂足分别为点H1，H2，H3．若PH1-PH2+PH3=3，请直接写出△ABC的面积．---Figure 1 (图1): Chart/Diagram Description: - Type: Geometric figure. - Main Elements: - A quadrilateral ABCD is shown. - A diagonal BD connects vertices B and D. - Point P is located on the diagonal BD. - A line segment PE is drawn from P, perpendicular to side AD at point E. - A line segment PF is drawn from P, perpendicular to side AB at point F. - Labels: A, B, C, D, P, E, F. - Angles: Right angle at E (PE ⊥ AD), right angle at F (PF ⊥ AB). - Text: 图1 (Figure 1). Figure 2 (图2): Chart/Diagram Description: - Type: Geometric figure. - Main Elements: - A rectangle ABCD is shown. - Point M is located on side AD. - Point N is located on side BC. - A triangle MBN is formed by connecting points M, B, and N. - Inside the triangle MBN, a quadrilateral EGFP is shown. - Point E is located on line segment MB. - Point G and point F are located on line segment BN, with G seemingly between B and F. - Point P is located on line segment MN. - Point C' is shown outside the rectangle and connected to B and N, forming a triangle NBC'. - Labels: A, B, C, D, M, N, E, G, F, P, C'. - Text: 图2 (Figure 2). Figure 3 (图3): Chart/Diagram Description: - Type: Geometric figure. - Main Elements: - A triangle ABC is shown. - Point P is located outside the triangle. - A dashed line extends from vertex A upwards. Point H1 is on this dashed line. A line segment PH1 is drawn from P to H1, perpendicular to the dashed line at H1. - Point H2 is located on side AC. A line segment PH2 is drawn from P to H2, perpendicular to AC at H2. - A dashed line extends from vertex C to the right, appearing to be an extension of side BC. Point H3 is on this dashed line. A line segment PH3 is drawn from P to H3, perpendicular to this dashed line at H3. - Labels: A, B, C, P, H1, H2, H3. - Dashed lines: A dashed line through A (containing H1), a dashed line extending from BC through C (containing H3). - Angles: Right angle at H1 (PH1 ⊥ line through A, H1), right angle at H2 (PH2 ⊥ AC), right angle at H3 (PH3 ⊥ line containing BC, H3). - Text: 图3 (Figure 3).