Question

coefficient of x power 20 in expansion of 1 - 2 x 4 whole power 7

Answer 1

Answer:

Step-by-step explanation:

(1 - x - x2 + x3)6

= (1 - x)6(1 - x2)6

= (6C0 - 6C1 x + ... + 6C6 x6)(6C0 - 6C1 x2 + ... + 6C6 x12)

Now, coefficient of x7 is  = 6C1 6C3 - 6C3 6C2+ 6C5 6C1

= – 144