Let Tn denote the number of triangles which can be formed using the vertices of a regular polygon of 'n' sides. If Tn+1-Tn=21, then 'n' equals - Share with your friends Share 16 Lovina Kansal answered this Dear student The number of triangles that can be formed byusing the vertices of a regular polygon is nC3. That is Tn=nC3Now, Tn+1-Tn=21⇒n+1C3-nC3=21⇒nC2+nC3-nC3=21 ∵n+1Cr=nCr-1+nCr⇒12n(n-1)=21⇒n=-6 or 7As n is a positive integer, n=7 Regards 90 View Full Answer Karan Thobhani answered this What do you mean Supurna Sadhukhan?? Can you please help answering the question?? -6