A polygon has 20 diagonals .how many sites it have?
ans 8 BUT HOW DO WE GET IT
http://www.mathsisfun.com/geometry/regular-polygons.html
Even i don't know but just memorize the formula n(n-3)/2 = No of diagonals.
Where n is the number of sides
To find the number of sides of a polygon given the number of diagonals, you can use the formula:
n(n-3) / 2 = d
Where "n" represents the number of sides and "d" represents the number of diagonals.
In this case, we know that the polygon has 20 diagonals. Therefore, we can plug in the value of "d" into the equation:
n(n-3) / 2 = 20
Now, we can solve for "n." Multiply both sides of the equation by 2 to eliminate the fraction:
n(n-3) = 40
Expand the equation:
n^2 - 3n = 40
Rearrange the equation to a quadratic form:
n^2 - 3n - 40 = 0
Now, we can try to factorize the quadratic equation:
(n - 8)(n + 5) = 0
Setting each factor equal to zero gives us:
n - 8 = 0 or n + 5 = 0
Solving each equation gives us:
n = 8 or n = -5
Since the number of sides of a polygon cannot be negative, we discard the n = -5 solution. Therefore, the polygon has 8 sides.