Find the number of sides of a regular polygon if one interior angle is 120 degrees
2 answers:
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Answer:
Step-by-step explanation:
In the diagram shown, the measure of angle 1 is oppositely directed to angle 2 and oppositely directed angles are equal.
Hence <1 = <3
Given < 1 = 3x-1 and <3 = 2x+9
Hence 3x-1 = 2x+9
collect like terms
3x-2x = 9+1
x = 10°
Since <1 = 3x-1
on substituting x = 10
<1 = 3(10)-1
<1 = 30-1
<1 = 29°
<1+<2 = 180 (angle on a straight line)
29+<2 = 180
<2 = 180-29
<2 = 151°
Similarly, on substituting x = 10 into <3
<3 = 2x+9
<3 = 2(10)+9
<3 = 20+9
<3 = 29°
<3+<4 = 180 (angle on a straight line)
29+<4 = 180
<4 = 180-29
<4 = 151°
