Cho tam giác ABC. Ba trung tuyến AM ; BN; CP cắt nhau tại G .Trên tia GM lấy điểm D sao cho MD = MG ,trên tia GN lấy điểm E sao cho NE = NG và trên tia GP lấy điểm F sao cho PF = PG. a) Chứng minh ∆ ABC = ∆ DEF
b) Chứng minh rằng G là trọng tâm của tam giác DEF

Which three lengths could be the lengths of the sides of a triangle? 21 cm, 7 cm, 7 cm 9 cm, 15 cm, 22 cm 13 cm, 5 cm, 18 cm 8 cm, 23 cm, 11 cm

David is spreading mulch on a triangular area of his flower bed. the coordinates of the vertices of the area are (1, 3), (9, 3), and (4, 6). what is the area of the triangle if each square has an area of 3 square feet?

Sarah took the advertising department from her company on a round trip to meet with a potential client. including sarah a total of 11 people took the trip. she was able to purchase coach tickets for $280 and first class tickets for $1280. she used her total budget for airfare for the trip, which was $6080. how many first class tickets did she buy? how many coach tickets did she buy?