Why are we using the a(n) thing to solve this? I do not quite get what it means by finding the derivate of a(n)1. Please do provide explanations as to why you are doing something particular. Little comments will be enough. Thank you so much!

7. Use the method of Frobenius to find y,(x) and y,(x) for x'y" +x(x' -3)y'+4y=0 Use a = - [( r + k) Pu - k + 9n-ka, *=0 F(r + n) to find an(r) and find a (r) (the derivative method) for a quick solution