Highly selective Backlog Qs for JEE MainMathematicsBinomial Theorem
If n is the degree of the polynomial, 2 5 x 3 + 1 - 5 x 3 - 1 8 + 2 5 x 3 + 1 + 5 x 3 - 1 8 and m is the coefficient of x n in it, then the ordered pair n , m is equal to
Options
- A8 , 5 10 4
- B12 , 8 10 4
- C12 , 20 4
- D24 , 10 8
Correct answer
C. 12 , 20 4
Step-by-step solution
2 5 x 3 + 1 - 5 x 3 - 1 8 + 2 5 x 3 + 1 + 5 x 3 - 1 8 Rationalizing denominators of both the brackets, = 5 x 3 + 1 + 5 x 3 - 1 8 + 5 x 3 + 1 - 5 x 3 - 1 8 = 2 8 C 0 5 x 3 + 1 8 + 8 C 2 5 x 3 + 1 6 5 x 3 - 1 2 + 8 C 4 5 x 3 + 1 4 5 x 3 - 1 4 + 8 C 6 5 x 3 + 1 2 5 x 3 - 1 6 + 8 C 8 5 x 3 - 1 8 = 2 5 x 3 - 1 4 + 28 5 x 3 + 1 3 5 x 3 - 1 + 70 5 x 3 + 1 2 5 x 3 - 1 2 + 28 5 x 3 + 1 5 x 3 - 1 3 + 5 x 3 + 1 4 So, n = 12 and m = 2 5 4 + 140 .5 3 + 70 .5 4 + 140 .5 3 + 5 4 = 160000 = 20 4