题目

一个三角形的两边长分别为3和6，第三边长是方程x2-10x+21=0的根，则三角形的周长为______________. 答案：【答案】16【解析】首先求出方程的根，再根据三角形三边关系定理，确定第三边的长，进而求其周长．解方程x2-10x+21=0得x1=3、x2=7，∵3＜第三边的边长＜9，∴第三边的边长为7．∴这个三角形的周长是3+6+7=16．故答案为：16．Complete the sentences with the given words in their proper forms（用括号中所给单词的适当形式完成下列句子）【1】This is the _______ time that I have read this interesting novel.（three）【2】Millions of ______ have come to Shanghai to enjoy themselves in Shanghai Disneyland.（visit）【3】The earthquake was so disastrous that many people were left _______（home）【4】They haven’t received any letters or e-mails from Wendy _________.（recent）【5】Learning and practicing will surely _______ us to make great progress.（able）【6】My father is thin and of average ______, yet he is a manager in a big company.（high）【7】In my opinion, ________ up is really harmful to our health.（stay）【8】After learning the text Mrs. White asked Mary to _______ it to the whole class.（told）