Trên tia Ox , vẽ hai điểm A,B sao cho OA = 2 cm , OB = 4 cm
a) Điểm A có nằm giữa hai điểm O và B không ?
b) So sánh OA và AB
c) Điểm A có là trung điểm của đoạn thẳng OB không ? Vì sao ?
K
Khách
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NM
Nguyễn Minh Quang
Giáo viên
21 tháng 12 2020
ta có
\(4\left(x^2+xy+y^2\right)\ge3\left(x+y\right)^2\Leftrightarrow\left(x-y\right)^2\ge0\) vì thế \(\sqrt{x^2+xy+y^2}\ge\frac{\sqrt{3}}{2}\left(x+y\right)\)
hoàn toàn tương tự ta sẽ có
\(P\ge\frac{\sqrt{3}}{2}\left(x+y\right)+\frac{\sqrt{3}}{2}\left(y+z\right)+\frac{\sqrt{3}}{2}\left(x+z\right)\)
hay
\(P\ge\sqrt{3}\left(x+y+z\right)=3\sqrt{3}\)
dấu bằng xảy ra khi x=y=z=1
KN
21 tháng 12 2020
Ta có: \(P=\sqrt{x^2+xy+y^2}+\sqrt{y^2+yz+z^2}+\sqrt{z^2+zx+x^2}\)\(=\sqrt{\frac{3}{4}\left(x+y\right)^2+\frac{1}{4}\left(x-y\right)^2}+\sqrt{\frac{3}{4}\left(y+z\right)^2+\frac{1}{4}\left(y-z\right)^2}+\sqrt{\frac{3}{4}\left(z+x\right)^2+\frac{1}{4}\left(x-y\right)^2}\)\(\ge\sqrt{\frac{3}{4}\left(x+y\right)^2}+\sqrt{\frac{3}{4}\left(y+z\right)^2}+\sqrt{\frac{3}{4}\left(z+x\right)^2}=\sqrt{3}\left(x+y+z\right)=3\sqrt{3}\)
Đẳng thức xảy ra khi x = y = z = 1
21 tháng 12 2020
I. Choose the best option A,B,C or D to complete the sentence
1 I wish I ______ people with the same interests
A.meet B.can meet C. could meet D.will meet
2. My mother says she used to _____ a diary when she was young.
A.keep B.use C.write D.preserve
3 The ______ between generations seems to be bigger and bigger than ever
A.blank B.space C.gap D.distance
4. Our teacher's is that we set up a project on preservation of our traditional games
A.offer B.suggestion C,scheme D.order
5 I found the letter in my bag. -I _____ to post it
A.forgot B.would forget C. was forgetting D. forgotten
6. Does he tell you how he is getting _____ his new colleagues?
A.on with B.on of C.away with D.out of
21 tháng 12 2020
7 Unfortunately the new system didn't _____our expectations
A. catch up with B. bring about C.come across D.come up to
8. The doctors say it'll take him a long to get _____ the shock
A.past B.above C.through D.over
9. I wish you ____ stop interrupting me whenever I speak.
A.will B.would C.could D.might
10. The policeman is happy ______ the kids safe and sound now.
A.finding B.be found C.to find D.have found
11. _______ she is young, she is very independent
A.Although B.because C.in order that D. in spite of
12. _______ he had finished his studies, he went to America
A.while B.before C.after D.until
