thanks you sorobon and thanks opalgHello, grgrsanjay!
Opalg gave you an excellent game plan . . . Did you follow it?
Rationalize the denominator . . . multiply top and bottom by the conjugate:
. .
. . . .
The sum becomes: .
. . . . . . . . . . . .
All terms cancel out . . . except the first and the last.
. . The sum is: .