Problem 30 of 34geo-030
A stop sign has the shape of a regular octagon: it has 8 equal sides and 8 equal angles. What is the measure of one interior angle of the sign?
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Solution walkthrough1:59
- Walk once around the sign. At each corner you turn by the outside angle. The turns make one full turn, .
- The turns are equal, so each outside angle is .
- At a corner, the outside and inside angles share a straight line, . So the inside angle is .
- Check: cuts from one corner make triangles. , and .
- Traps: is the outside angle. is all angles together. forgets to subtract from .