The term independent of x in the binomial expansion of 1 - 1 x + 3 x 5   2 x 2 - 1 x 8 is

The term independent of x in the binomial expansion of 1-1x+3x5 2x2-1x8 is
  1. - 496
  2. -400
  3. 496
  4. 400

Solution

The term independent of x will come from

1-1x+3x52x2-1x8

General term of  2x2-1x8 is C 8 r ( 1 x ) r  2x28-r= C 8 r 2 8r (1) r x 163r

From expansion

12x2-1x8-1x2x2-1x8+3x52x2-1x8

12x2-1x8 no constant term

-1x2x2-1x8 for constant term

 r=5   C 8 3 2 3 (1) 5 =+448

3x52x2-1x8 for constant term

r=7 C 38 7 2 1 (1) 7 =48

Hence, term independent from x=448-48=400
 

Asked in: JEE Main 2015 (11 Apr Online)

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