Question

英语数学题求助！急！！谢谢~~

1.Find the first three terms in the expansions,in ascending powers of x,of (1-2x))^16
2.Find the coefficient of a^3b^5 in the expansions of (5a+1/2b)^8

Answer 1

1.the first three terms of (1-2x)^16 are : 1 , -32x , 480x^2
2.the term consists of a^3b^5 is : C(8,3)*(5a)^3*(b/2)^5
so the coefficient of it is : C(8,3)*5^3 / 2^5 which is equal to 6968

Answer 2

1.Find the first three terms in the expansions,in ascending powers of x,of (1-2x))^16
2.Find the coefficient of a^3b^5 in the expansions of (5a+1/2b)^8