Binomail theorem finding the coefficient of x^20 term in an rational index expansion with whole power 3..image for question is attached..

Dear Student,
To find the coefficient of x²⁰ in the given exantion, we can replace the terms written in the bracket with the (e^x -(higher power of x))³. Now the coefficient of x²⁰ will lies in the (e^x)³ (= e^3x) only. Now the exponential series has 3x in place of x. therefore the coefficient of x²⁰ will be 3²⁰/20!
Thanks.