Answer is (B) 6
In the expansion of (1 + x)18 coefficients of (2r + 4)th and (r – 2)th terms are 18C2r + 3 and 18Cr – 3 respectively
Given :
These are equal
Then, 18C2r + 3= 18Cr – 3
⇒ 2r + 3 = r – 3
or 2r+ 3= 18 -(r – 3)
For using the statement if
nCr = nCp or nCn-p
⇒ 2r – r = -3 – 3
or 2r + 3 = 18 – r + 3
⇒ r = -6 or r = 6
r is a natural number, so r = – 6 is not possible, then x = 6.