(1)∵在△ABC中,∠A=70°,∠ACB=40°,
∴∠ABC=180°-∠A-∠ACB=70°,
∵BD、CE分别是∠ABC、∠ACB的平分线,
∴∠OBC=
1
2 ∠ABC=35°,∠OCB=
1
2 ∠ACB=20°,
∴∠BOC=180°-∠OBC-∠OCB=125°;
(2)∠BOC的大小不发生变化.
∵BD、CE分别是∠ABC、∠ACB的平分线,
∴∠OBC=
1
2 ∠ABC,∠OCB=
1
2 ∠ACB,
∴∠BOC=180°-∠OBC-∠OCB,
=180°-
1
2 (∠ABC+∠ACB),
=180°-
1
2 (180°-∠A),
=90°+
1
2 ∠A=125°,
∴∠BOC的大小只与∠A的大小相关.