(a)Compute (i) `(20!)/(18!)` (ii) `(10!)/(6!.4!)` (b)find n if `(n+2)! =2550*n!`

If (n+2)!=2550n!, then n

Evaluate. (i) i^(1998) (ii) i^(-9999) (iii) (-sqrt-1)^(4n=3) ,n ne N

If P(n,4)=20P(n,2), find n

Evaluate (n!)/((n-r)!) when : (i) n=10,r=4 (ii) r = 1 (iii) r = 2.

If P(n,4)=20xx P(n,2), find n

Find n, if (n+2)!=2550xx n!(ii)(n+1)!=12xx(n-1)!

(i) If (n!)/(2.(n-2)!): (n!)/(4!.(n-4)!) = 2:1 , find the valye of n. (ii) If ((2n)!)/(3!(2n-3)!): (n!)/(2!(n-2)!) = 44:3 , then find the value of n.

Find the sum of n terms of the series (1)/(2*4)+(1)/(4*6)+... (A) (n)/(n+1) (B) (n)/(4(n+1)) (C) (1)/((2n)(2n+2))( D) )(1)/(2^(n)(2^(n)+2))