One plane is 20 km from the Winnipeg Airport. A larger plane is 17 km from the airport. If the angle between the sightings is 110 degrees, how far apart are the planes?The Problem:

First, I drew a triangle.Attempted Solution:

Then I used the law of cosines.

Then put in the , , and values.

So the answer should be 21.06 km. But, according to the answer key, it's 30.36 km. I cannot figure out where I erred. Could someone please help?