Question

find the cofficient of x^18 of (x²+ 3a/x)15​

Answer 1

Step-by-step explanation:

Here x → x2 a → 3ax3ax, n =15 ∴ Tr+1 = 15Cr.(x2)15-r(3ax3ax)r

= 15Crx30-2r.(3a)rxr = 15Cr .3r .ar .x30-3r

To find the coefficient of x18,

we get 30 – 3r = 18 12 = 3r ⇒ r =4

∴ T4+1 = 15C4.34 .a4 .x18

∴ coefficient of x18 is 15C4.(3a)

Answer 2

Answer:

the cofficient of x^18 of (x²+ 3a/x)15 =15C11(3a)^4