Most Important Selected Qs for JEE AdvancedMathematicsPermutation and Combination
Let T_n be the number of all possible triangles formed by joining vertices of an n- sided regular polygon. If T_ n+1 -T_n=10 then the value of n is:
Options
- A10
- B8
- C7
- D5
Correct answer
D. 5
Step-by-step solution
As we know, n sides polygon has ^n C₃ number of triangles aligned & ^ n+1 C₃- ^n C₃=10 & n ( n -1)=20 & n ^2- n -20=0 & n =-4,5 aligned