Consider the differentisl equation: x 2
(x+1)y ′′
+4x(x+1)y ′
−6y=0,x>0, near x 0
​
=0. Let r 1
​
,r 2
​
be the tro roots of the indicial equation, then r 1
​
+r 2
​
= a) −6 b) −4 c) −2 d) −5 e) −3