a) Từ M kẻ thêm đường trung bình MQ và song song với cạnh BD

Vì MQ là đường trung bình của tam giác BDC

=> DQ = QC (1)

Xét tam giác AMQ:

Vì I là trung điểm AM ( gt )

Mà MQ song song với BD hay MQ song song với ID

=> D là trung điểm AQ

=> AD = DQ (2)

Từ (1) và (2) ta có:
DQ =QC, AD = DQ

=> DQ = QC = AD

=> AD = 1/2 DC

Living a healthy lifestyle brings many important benefits to our lives. It helps us stay physically strong, improve our immune system, and reduce the risk of serious diseases. Regular exercise and a balanced diet also support mental health by reducing stress and increasing happiness. Moreover, healthy habits improve concentration and energy, allowing us to study and work more effectively. Overall, a healthy lifestyle helps us enjoy life longer and more actively.

Living a healthy lifestyle brings many important benefits to our lives. It helps us stay physically strong, improve our immune system, and reduce the risk of serious diseases. Regular exercise and a balanced diet also support mental health by reducing stress and increasing happiness. Moreover, healthy habits improve concentration and energy, allowing us to study and work more effectively. Overall, a healthy lifestyle helps us enjoy life longer and more actively.

Living a healthy lifestyle brings many important benefits to our lives. It helps us stay physically strong, improve our immune system, and reduce the risk of serious diseases. Regular exercise and a balanced diet also support mental health by reducing stress and increasing happiness. Moreover, healthy habits improve concentration and energy, allowing us to study and work more effectively. Overall, a healthy lifestyle helps us enjoy life longer and more actively.

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