The formula for circumference is

.
To express the circumference exactly, plug the diameter in for

and put the

symbol in front of it. Don't multiply. This expresses the exact circumference.
Say you have the diameter of 17.
You can express the circumference with 17

.
Answer: 
Step-by-step explanation:


Normally we wouldn't have our square variable be negative, so in order to get rid of that negative sign without changing the equation is by multiplying by -1

Answer: 80 miles
Step-by-step explanation:
10mph + 30mph = 40 mph
Distance = Speed × time
D = 40m/h × 2 h
D = 80 m