Answers

2016-02-18T11:13:12+05:30
Ok, both the D and F angles are similar because DE=EF, so you can say that angleD=angleF
now as everyone knows the sum of three angles is 180 degrees, so....

angleD+angleE+angleF=180
[you can put angleD in place of angleF because both are similar]
so, 
angleD+angleD+angleF=180
2*angleD+30=180
2*angleD=180-30
2*angleD=150
angleD=150/2=75
so, here we have got the value of angleD which is 75 degrees. Hope it helped, [and what is anh?]
ok, here's what you want.
firstly, construct De=5cm.
2.the construct 
∠E which is 30 degrees.
3.and finally make an arc on EF↔ with the measurement of 5 cms.
3.then construct DF which will be of 5 cms exactly.
4.m
∠D=75 [how? It's already mentioned above]

0
he asked for the construction , not the proof
send him the steps of construction
oh lol it's a construction
ok wait a minute