I don't understand the procedure you're using . . .
. . First Derivative Test for the "left side"?
. . Second Derivative Test for the "right side"?
Who told you to do it that way ??
Set the first derivative equal to zero: .Find and identify the stationary points for: .
. . which factors:. .
. . and has roots: .
Stationary points: .
Second Derivative Test: .