Because DE is parallel to BC, angle EDA = angle B, so angle EDA = angle A; So △ADE is an isosceles triangle;
7.( 1) Because DG = EF and DC = BE, Rt△CDG is equal to Rt△BEF;; ; So CG = BF
So CG-GF=BF-GF So: CF = BG.
(2) Because BG=CF and DG = EF, Rt△BDG is all equal to Rt△CEF;; ; So BD = ce
8. Set the angle to o; Because bo = 0.7 and ab = 2.5, ao = (2.5 square -0.7 square) root = 2.4;
So a1o = 2.4-0.4 = 2; So B 1o = (2.5 square -2 square) root =1.5;
So b moves outward: 1.5-0.7 = 0.8.