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In our city, there is a big zoo. There are a lot of different animals in it. There are some scary(吓人的) tigers and lions. They like eating meat and they eat much meat every day.
There are also two big elephants and a baby(幼崽) one. Children like to ride one of them. The elephants are very kind and friendly. They eat much grass and bananas.
In the zoo, we can see different kinds of bears(熊): brown bears, black bears and white bears. They are all shy and clumsy(笨拙的). They stand on their back legs and lift their front legs to ask for food They like cakes very much.
Do you like pandas? There's only one in the zoo. Her name is Lingling. She is very cute. She likes eating bamboos a lot. She is kind of shy, She's very interesting and lovely.

如图，在直角坐标系xOy中，点A在第一象限，点B在x轴的正半轴上，△AOB为正三角形，射线OC⊥AB，在OC上依次截取点P₁，P₂，P₃，…，P_n，使OP₁=1，P₁P₂=3，P₂P₃=5，…，P_n﹣1P_n=2n﹣1（n为正整数），分别过点P₁，P₂，P₃，…，P_n向射线OA作垂线段，垂足分别为点Q₁，Q₂，Q₃，…，Q_n，则点Q_n的坐标为____ ．

代数式  $-3-\sqrt{a+b}$的最大值为____.  

已知Rt△ABC中，∠C=90°，CH⊥AB于点H，AC=3，CH=2，求BC的长．