Question

If the coefficients of (2r + 4)^th, (r – 2)^th terms in the expansion of (1 + x)¹⁸ are equal, then r is ______.

Options

• 4

• 6

• 8

• 3

Answer 1

If the coefficients of (2r + 4)^th, (r – 2)^th terms in the expansion of (1 + x)¹⁸ are equal, then r is 6.

Explanation:

Given that `""^18C_(2r + 3) = ""^18C_(r - 3)`

⇒ 2r + 3 + r – 3 = 18

⇒ r = 6