Question

5. A polygon has 90 diagonals. How many triangles can be formed through the vertices of the polygon?

Answer 1

n(n-3)/2 <--- n gives the no of vertices (perhaps)

Answer 2

n = 15 (perhaps)
http://www.wolframalpha.com/input/?i=n%28n-3%29%2F2+%3D+90

Answer 3

A. 2730
B. 455
C. 220
D. 1320

Answer 4

thse are options

Answer 5

looks like i got it wrong.

Answer 6

let's try for pentagon,

Answer 7

no you were right, the polygon has 15 sides (vertices)
# triangles = #sides choose 3 ,since you need 3 vertices to make a triangle

--> 15C3 = 455

Answer 8

well, that solves it :)

Answer 9

7. What is the sum of cubes of roots of the equation x2 − x + 1 = 0?

Answer 10

find the root first

Answer 11

please help me