Question

In the expansion of (ax+1)^7
the fifth term is 945x^3
Find the value of a.

Answer 1

Answer:

a = 3

Step-by-step explanation:

First start writing out the binomial expansion of $(ax + 1)^7$

$[1^7] + [7C1 * 1^6 *(ax)] + [7C2*1^5*(ax)^2]+[7C3*1^4*(ax)^3]$

as you can see from this, the last bracket will produce our $x^3$ term

$7C3*1^4*a^3x^3 \\35a^3x^3\\35a^3 = 945\\a^3 = 27\\a = 3$

Hope this helps, let me know if you have any questions :)