20 1 1 is "nine? On the 80th anniversary of the "18th Incident", a student union cadre of a university history department organized volunteers to come to Changchun Sculpture Park on September 20th118th.
OB=5cm,OA= 12cm,
According to Pythagorean theorem, AB=OB2+OA2= 13cm,
∫AB < 15cm,
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