四边形内角和∠A+∠B+∠C+∠D=360°
∠A+∠C=180°
则∠B+∠D=180°
∠B:∠D=4:6
则∠B=4/10×180°=72°
∠D=6/10×180°=108°
∠B:∠C=4:5
∠C=5/4×∠B=90°
∠A=180°-∠C=90°
四边形内角和∠A+∠B+∠C+∠D=360°
∠A+∠C=180°
则∠B+∠D=180°
∠B:∠D=4:6
则∠B=4/10×180°=72°
∠D=6/10×180°=108°
∠B:∠C=4:5
∠C=5/4×∠B=90°
∠A=180°-∠C=90°