The number of diagonals in a certain regular polygon is equal to four times the number of sides. How many sides does this polygon have?
There was a question similar to this except it was 5 times the number of sides, please help me.
The formula for the number of diagonals of a polygon is: n(n - 3) / 2 (where n is the number of sides)
So, the equation is; n(n - 3)/2 = 4n
Multiplying both sides by 2: n(n - 3) = 8n
Solving: n2 - 3n = 8n
n2 - 11n = 0
n(n - 11) = 0
Since a polygon can't have 0 sides; the answer is: 11 sides