Xét tam giác ABC có hai đường trung tuyến BM và CN cắt nhau tại G.

Suy ra G là trọng tâm tam giác ABC

=> BG=2/3 BM;CG=2/3CN

=>BM=3/2BG;CN=3/2 CG.

Do đó ta phải chứng minh 3/2 BG+3/2 CG>3/2 BC hay BG+CG>BC(1)

Bất đẳng thức (1) luôn đúng vì trong tam giác tổng độ dài hai cạnh lớn hơn độ dài cạnh còn lại.

Vậy BM+CN>3/2BC

Question 1:Last night,I didn't order milkshake because I wasn't thirsty

Question 2:How time you spend on math homework each day?

Question 3:Eating fruits and vegetables is the healthiest way stay fit

question 1:We planted trees in the community garden a month ago

question 2:Her voice is as beautiful as a melody from a fairy tale

question 3:We have a school assembly in the school yard on Monday mornings

Question 1: I fancy pat in a clean-up this month

Question 2: The bookshellevs are some high as the windows.

Question 3:Why don'we collect old phastic bottles and paper in our school.

Question 4:My friends go to the studio to practice dancing.And i do it too.