It also could be solved without using auxiliary line ED. AF =AEcos(x) Then we have AD = 2AF = 2AEcos(x) Let's now use Law of sines for triangle ADC : 2AEcosx/sin(DCA)=DC/sinx 2sinxcosxAE=sinDCA*AE sin(2x) = sin(DCA) DCA = 2x Then for triangle ABC we have 30+30+60+x+2x=180 3x=60 x=20
It also could be solved without using auxiliary line ED.
AF =AEcos(x) Then we have
AD = 2AF = 2AEcos(x)
Let's now use Law of sines for triangle ADC :
2AEcosx/sin(DCA)=DC/sinx
2sinxcosxAE=sinDCA*AE
sin(2x) = sin(DCA)
DCA = 2x
Then for triangle ABC we have
30+30+60+x+2x=180
3x=60
x=20