Question

Let $a_1 a_2 a_3 \dotsb a_{10}$ be a regular polygon. A rotation centered at $a_1$ with an angle of $\alpha$ takes $a_4$ to $a_8$. Given that $\alpha < 180^\circ$, find $\alpha,$ in degrees

Answer 1

Answer:

  72°

Step-by-step explanation:

The required angle of rotation can be found by considering the regular polygon to be inscribed in a circle. Each of its 10 vertices will be separated by a central angle of 360°/10 = 36°. So, the vertices a8 and a4 will be separated by a central angle of (8 -4)(36°) = 144°.

The angle a4-a1-a8 is an inscribed angle, so will have half the measure of the central angle intercepting the a4-a8 arc. The desired angle of rotation to map a4 to a8 is ...

  α = 144°/2 = 72°