Polygon diagonal sides

Determine the type of polygon if the number of all diagonals is 90.

(Write down the number of its pages.)

Final Answer:

n =  15

Step-by-step explanation:

u=90  u = 2n (n3)  2 u=n (n3)  2 90=n (n3) n2+3n+180=0 n23n180=0  a=1;b=3;c=180 D=b24ac=3241(180)=729 D>0  n1,2=2ab±D=23±729 n1,2=23±27 n1,2=1.5±13.5 n1=15 n2=12  n=n1=15

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