Answer:
5
Step-by-step explanation:
Use the distance formula 
insert the numbers into the formula 
2+1=3 and 0-4=-4
=9 and
= 1
9+16=25
the square root of 25 is 5
Answer:
ABC is more than 90 Degrees because it is an Obtuse Angle
ADC is less than 90 Degrees because it is an Acute Angle
I don't know the exact answer but I hope this helps you a little!