If ARC CD = 143°, and ARC AB = 39°, what is m∠DEC?

https://media.glynlyon.com/g_geo_2012/13/img_geou13a_54.gif

88°
89°
90°
91°

Question

If  ARC CD = 143°, and ARC AB = 39°, what is m∠DEC?

https://media.glynlyon.com/g_geo_2012/13/img_geou13a_54.gif

88°
89°
90°
91°

anonymous · Answer

m∠DEC = (ARC DC + ARC AB) / 2 
now I think you can find the answer...

ttop0816 · Answer

@PFEH.1999 then do you think you could help me out with this question too?? If ARC AC = 80°, and m∠BED = 25°, what is ARC BC ? https://media.glynlyon.com/g_geo_2012/13/img_geou13a_56.gif 55° 30° 65° 20°

anonymous · Answer

Yes!
m∠BED = (ARC AC - ARC BD) /2

ttop0816 · Answer

so would the equation be 80 - 25 over 2??

anonymous · Answer

m∠BED = 25
ARC AC = 80
so:
25 = (80 - ARC BD) / 2 --> 80 - ARC BD = 25x2 --> 80 - ARC BD = 50
-->  80 - 50 = ARC BD --> ARC BD = 30

anonymous · Answer

@ttop0816 , Did you get it?