I have a circle with a Tangent line, DE, running along it and connecting with another line, FC, which runs through the center of the circle to the other side.I have connected the center of the circle with point E on the edge of the circle with a radius. I have labeled the center of the circle O.

Question

I have a circle with a Tangent line, DE, running along it and connecting with another line, FC, which runs through the center of the circle to the other side.I have connected the center of the circle with point E on the edge of the circle with a radius. I have labeled the center of the circle O. 
Angle D equals 40 degrees. Angle DEO equals 90 degrees. Angle FOE equals 50 degrees.

What is arc measure EF?

MathMate · Answer

Double post. See answer by Reiny: http://www.jiskha.com/display.cgi?id=1244076544