JEE Main20199 Apr 2019Morning ShiftMathematicsMatricesActual
If 1 1 0 1 1 2 0 1 1 3 0 1 … . 1 n - 1 0 1 = 1 78 0 1 , then the inverse of 1 n 0 1 is:
Options
- A1 – 12 0 1
- B1 0 12 1
- C1 0 13 1
- D1 – 13 0 1
Correct answer
D. 1 – 13 0 1
Step-by-step solution
Given 1 1 0 1 1 2 0 1 1 3 0 1 . . . . 1 n - 1 0 1 = 1 78 0 1 And, we have 1 1 0 1 1 2 0 1 = 1 3 0 1 = 1 1 + 2 0 1 Also, 1 1 0 1 1 2 0 1 1 3 0 1 = 1 3 0 1 1 3 0 1 = 1 6 0 1 = 1 1 + 2 + 3 0 1 ⇒ 1 1 0 1 1 2 0 1 1 3 0 1 . . . . 1 n - 1 0 1 = 1 1 + 2 + 3 + . . . . + n - 1 0 1 ⇒ 1 1 + 2 + 3 + . . . . + n - 1 0 1 = 1 78 0 1 Using the sum of first n natural numbers i.e. 1 + 2 + 3 + . . . + n = n n + 1 2 , we get n ( n - 1 ) 2 = 78 ⇒ n 2 - n - 156 = 0 ⇒ n - 13 n + 12 = 0 ⇒ n = 13 or n = - 12 (r