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The regular pentagon shown is rotated clockwise about center point P.

●P
Choose all degrees of rotation that will carry the regular pentagon onto itself.
A. 72°
B. 90°
C. 108°
D. 144°
E. 216°

The regular pentagon shown is rotated clockwise about center point P. ●P Choose all-example-1
User Keith Lyall
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2 Answers

20 votes
20 votes

Answer:

A. 72°

D. 144°

E. 216°

Explanation:

are you tempted to calculate the internal angles ?

that is, I guess, the trap set by your teacher here, and it would be the wrong approach.

nevertheless, quickly just as a reminder :

the sum of all internal angles in a polygon is

(n - 2)×180°

n being the number of sides.

in our case that is

(5 - 2)×180 = 3×180 = 540°

so, each internal angle is 540/5 = 108°.

but we are not turning at an edge or vertex. no, we are turning the pentagon around is central point.

we are running each vertex along a circle arc. the center of that circle being P.

after every 1/5 of the circle arc there is a vertex of the pentagon.

and whenever we rotate one vertex on top of the next one, we carry the pentagon visually onto itself.

so, instead of a full circle rotation we need only 1/5 of that :

360 / 5 = 72°

and with every additional 1/5 of the circle arc (or 72°) we get it again.

that means at

72°

144°

216°

288°

360°

the pentagon carries onto itself.

therefore, A, D and E are correct.

User SpaceFozzy
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3.2k points
17 votes
17 votes
You’re answer is Choice number c
User Foka
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2.9k points