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primary 6 | Maths | Geometry
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Gens
Gens

primary 6 chevron_right Maths chevron_right Geometry chevron_right Singapore

2017 SA2 Red swastika

Date Posted: 4 years ago
Views: 363
Marilyn Chew
Marilyn Chew
4 years ago
Hello JO,

The formula for the sum of the interior (inside) angles of a polygon (shape) is (n-2) x 180 degrees. n is number of sides in the polygon.

Eg. Triangle has 3 sides (n=3), sum of interior angles of triangle is (3-2) x 180, which is 1 x 180 = 180 degrees.

This shape is a pentagon (5 sides). Sum of interior angles is (5-2) x 180 degrees = 3 x 180 degrees = 540 degrees.

Pentagon has equal sides and angles (question says so), so each angle is 540/ 5 (540 divide by 5) = 108 degrees.

Answer is 108 degrees, option 3 :)
Gens
Gens
4 years ago
thanks so much. you are correct
Marilyn Chew
Marilyn Chew
4 years ago
Most welcome, all the best!

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AC Lim
Ac Lim's answer
12510 answers (A Helpful Person)
1st
Hope this helps
Gens
Gens
4 years ago
thanks a lot
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AC Lim
Ac Lim's answer
12510 answers (A Helpful Person)
Total have 5 same angle in pentagon (5 sided figure which have all equal sides and angle).
Therefore divide 5.
Hope this helps.
J
J
4 years ago
Most intuitive method. Great job
AC Lim
AC Lim
4 years ago
Since the student mentioned ---> have not learn this yet, therefore have to introduce this(Triangle) method. (Angle each triangle = 180). So they no need to remember formula (n-2)x180.
Thanks J. Noticed you done lot of great job too (in other question). Learnt a lot from you too.
J
J
4 years ago
Yes this is the best for primary school, the formula is typically taught at secondary level only.

Am learning a lot from you as well, your solutions help me to see the question and solving approach in new perspectives. Kudos!