**Question:**

Give five rays Ox, Oy, Oz, Ot, On in that order with the same O root. Prove that in the angles $ \widehat {xOy} $; $ \widehat {yOz} $; $ \widehat {zOt} $; $ \widehat {tOn} $; $ \widehat {nOx} $ must have at least one angle whose measurements do not exceed $ 72 ^ o $.

**Answer**

Assuming that all given $ 5 $ angles have measurements greater than $ 72 ^ \circ $, such a total of $ 5 $ angles must be greater than $ 72 ^ \circ .5 = 360 ^ \circ $. This is absurd.