Answer:
Step-by-step explanation:
If BD_|_AC
in trg BDA ,sin 45=BD/40=V2/2
BD*2=40V2
BD=40V2/2=20V2 and AD=BD
so CD=30-AD=30-20V2
in trg BCD, BC^2=BD^2+CD^2
BC^2=(20V2)^2+(30-20V2)^2=
(20V2)^2+30^2-2*30*20V2+(20V2)^2=
400*2+900-1200V2+400*2=
800+900-1200V2+800=
2700-1200V2
so BC=V100(27-12V2)=10V(27-12V2
