Okay, now without the "celcius", one needs to determine the radius at the given latitude. This is no problem with just a little trigonometry.
Draw a circle.
Put in a horizontal diameter representing the side view of the Equator.
Point out the Center. Call it point "O".
Label half this diameter 6373 km.
Put in another Radius somewhere between the equator and a Pole.
Label this new radius 6373 km (We just assumed the earth is a perfect sphere. Oh, well.)
Lable the point of intersection of the new radius and the circle "A".
Construct a line segment perpendicular to the Equator and to point "A".
Label the point where the new line segment intersects the Equator "B".
Notice a couple of things.
Triangle ABO is a Right Triangle.
Angle BOA is your lattitude measurement.
Segment OB is your radius for the lattitude measurement.
You need only a cosine to calculate the length of OB.
You're on your way.