∴∠B=∠C=45
AE = CF
∴E is the midpoint of AB and F is the midpoint of AC.
∴AE=BE=AF=FC
∫D is the midpoint of BC, ∠ B = ∠ C = 45.
∴ED=DF
∫∠A = 90，ED=DF
A quadrilateral is a square.
∴de⊥df<； /pre & gt；
& ltdiv class = " replyask-box u-276974952-e " id = " replyask-7457979 " >
& lth4 class="ask "> requirements
& ltdiv class="replyask-content " >
& lt preclass = "reply ask-text" id = "content-7457979" > e is any point on AB and f is any point on AC.
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& ltdiv class = " replyask-box u- 120750490-e " id = " replyask-7458392 " >。
& lth4 class="reply "> answer.
& ltdiv class="replyask-content " >
& lt preclass = "replyask-text" id = "content-7458392" > try your best.
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& ltdiv class = " replyask-box u-276974952-e " id = " replyask-7458566 " >
& lth4 class="ask "> requirements
& ltdiv class="replyask-content " >
& lt preclass = "replyask-text" id = "content-7458566" > I am in grade one, can I use congruent triangles's method?
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& ltdiv class = " replyask-box u- 120750490-e " id = " replyask-7458848 " >。
& lth4 class="reply "> answer.
& ltdiv class="replyask-content " >
& lt preclass = "replyask-text" id = "content-7458848" > It is simple to solve this problem, and congruent triangles's method is feasible, but it will complicate the problem.
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& lt/div & gt；
& ltdiv class = " replyask-box u-276974952-e " id = " replyask-7458887 " >
& lth4 class="ask "> requirements
& ltdiv class="replyask-content " >
& lt preclass = "replyask-text" id = "content-7458887" > what is the general idea?
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& ltdiv class = " replyask-box u- 120750490-e last " id = " replyask-745922 1 " >
& lth4 class="reply "> answer.
& ltdiv class="replyask-content " >
& lt preclass = "replyask-text" id = "content-7459221"> it is known that Rt△AB, AC isosceles right triangle e, f, d are AB, AC, BC have midpoint △BED and △DFC are congruent triangles.
∠ b =∠ c = 45, then ED=DF, ed ∠ dfnwh.