Question

已知三角形内角A.B.C的关系为:角A+2角B-角C=30度,2角A+角C-角B=180度,求角A,B,C各=?

Answer 1

∠A+2∠B-∠C=30°① 2∠A+∠C-∠B=180°② ∠A＋∠B+∠C=180°③ ②-③得 ∠A-2∠B=0 ∠A=2∠B④ 代入①②得 4∠B-∠C=30° 3∠B+∠C=180° 解得∠B= 30° ∠C=90° ∠A=2∠B=60°