是人教版的哦
(1)因为∠BGC=180°-(∠GBC+∠GCB) (三角形内角和180°)
而∠GBC=1/2∠ABC;∠GCB=1/2∠ACB
所以:∠BGC=180°-1/2(∠ABC+∠ACB)
(2)因为180°-∠A=∠ABC+∠ACB
所以∠BGC=180°-1/2(∠ABC+∠ACB)=180°-1/2(180°-∠A)
=180°-90°+∠A=90°+∠A