The number of values of ' r ' satisfying the equation, 39 C3 r-1- 39 Cr2= 39 Cr2-1- 39 C3 r is :

Question

The number of values of ' r ' satisfying the equation, 39 C3 r-1- 39 Cr2= 39 Cr2-1- 39 C3 r is : (A) 1 (B) 2 (C) 3 (D) 4

Tardigrade Admin · Accepted Answer

39 C 3 r -1- 39 C r 2= 39 C r 2-1- 39 C 3 r ⇒ 39 C 3 r -1+ 39 C 3 r = 39 C r 2-1+ 39 C r 2 40 C 3 r = 40 C r 2 r 2=3 r or r =0,3

Q. The number of values of ' $r$ ' satisfying the equation, $^{39} C_{3 r - 1} -^{39} C_{r^{2}} =^{39} C_{r^{2} - 1} -^{39} C_{3 r}$ is :