limx→asin√x−sin√ax−a
=limx→asin√x−sin√a(√x−√a)×(√x+√a)
=limx→a2 sin(√x−√a2)cos(√x+√a2)(√x−√a)×(√x+√a)
=2(limx→asin√x−√a2(√x−√a2))×12limx→acos(√x+√a2)limx→a(√x+√a)
=2×1×12×cos√a×12√a
=cos√a2√a