(a)∵AB平行于CD,PA BQ分别垂直DC于P Q∴ABQP为矩形∴PQ=AB=11QC=CD-DP-PQ=36-x-11=25-x(b)x^2+h^2=25^2(25-x)^2+h^2=30^2∴25^2-x^2=30^2-(25-x)^225^2-x^2=30^2-25^2+50x-x^250x=25^2+25^2-30^2x=7h^2=25^2-x^2=25^2-7^2=576h=24(c) S=(11+36)*24/2=564