While working on a problem, I had to look up a formula for the area of a circle segment. I have noticed that there is some ambiguity in the results.

According to Wolfram Alpha, the formula is:

Attachment 18691

According to two other sources, the formula is:

½r^2(θ × pi/180)

Wolfram Alpha has been very reliable in the past, however I would prefer to not get this wrong due to a formula error. Please clarify which or what is correct. Thanks.