混合物
纯净物
单质
电解质
A
盐酸
NaOH
石墨
K2SO4溶液
B
空气
Fe(OH)3胶体
铁
Na2CO3
C
CuSO4•5H2O
CaCl2
水银
铜
D
氯水
KNO3晶体
O3
NaCl
A:A
B:B
C:C
D:D
九年级学生王涛来到商店想买一张学习用的光盘,营业员告诉他,如果买正版的,要20元一张;如果买盗版的,只要5元一张。你认为王涛正确的做法应该是( )①购买正版,拒绝盗版②告诉营业员盗版光盘侵犯了他人的智力成果权③及时向有关部门举报④盗版便宜,如果家庭经济状况不好,可以购买
A. Red is my favourite colour.
B. What time does the party begin?
C. That sounds interesting.
D. It's on 5th January.
E. Can you come to my birthday party, Linda?
Peter: ____
Linda: Sure. When's your birthday?
Linda: ____
Peter: It begins at half past six in the evening.
Linda: OK.
Peter: Please bring some red things to the party. It's a "red party". ____Linda: A “red party”? ____ I can't wait.
请阅读下列材料:若两个正实数a1,a2满足a12+a22=1,那么a1+a2≤ 2 .
证明:构造函数f(x)=(x-a1)2+(x-a2)2=2x2-2(a1+a2)x+1,因为对一切实数x,恒有f(x)≥0,所以Δ≤0,从而得4(a1+a2)2-8≤0,所以a1+a2≤ 2 .
根据上述证明方法,若n个正实数满足a12+a22+…+an2=1时,你能得到的结论为____.