Question

在△ABC中,AB=AC,以AB为直径的圆O交AC与于点D,DF⊥BC,交AB的延长线于点E.当cosE=4/5.BF=

Answer 1

设BC边上的高是AH

cosE=4/5 ,BF=6

EF=8 ,EB=10

∠BAC=2∠E

cos∠BAC= 2cos²∠E-1 = 7/25 ,sin∠BAC=24/25

BD=5/4*BF = 15/2

AB=BD/sin∠BAC = (15/2) ÷ ( 24/25) = 125/16