Test Index

BECE Mathematics 2010 Paper

Question : 29

Total: 40

120^{\circ}

Solution:

\; \text{ Interior angle } \;=\; \frac{(n-2)\times 180}{n}

Where

n=

number of sides of the polygon.

Interior angle

=120^{\circ}

\; \frac{(n-2)\times 180}{n}=120

Get rid of the fraction by multiplying both sides by

n

\; (n-2)\times 180 = 120 \times n

\; n \times 180 - 2 \times 180 = 120 \times n

\; 180 n - 360 = 120 \times n

\; 180 n - 120 \times n = 360

\; 60 n = 360

Divide both sides by 60

n = \; \frac{360}{60}

Note:

1. The zero ( 0 ) at the end of 360 and 60 cancels each other

2. 6 divides itself 1 and 36,6 times

n = 6

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