HỦY DIỆT THE WORLD
03/12/2017 at 21:52-
KEITA FC 8C 03/12/2017 at 22:04
Ta có :
\(p=\sqrt{\dfrac{ab}{\left(1-a\right)\left(1-b\right)}}+\sqrt{\dfrac{bc}{\left(1-b\right)\left(1-c\right)}}+\sqrt{\dfrac{ac}{\left(1-a\right)\left(1-c\right)}}\)
Theo Bất Đẳng Thức Cosi ta có :
\(2\sqrt{\dfrac{ab}{\left(1-a\right)\left(1-b\right)}}=2\sqrt{\dfrac{a}{1-b}\times\dfrac{b}{1-a}}\le\dfrac{a}{1-b}+\dfrac{b}{1-a}\)
\(2\sqrt{\dfrac{bc}{\left(1-b\right)\left(1-c\right)}}=2\sqrt{\dfrac{b}{1-c}\times\dfrac{c}{1-b}}\le\dfrac{b}{1-c}+\dfrac{c}{1-b}\)
\(2\sqrt{\dfrac{ac}{\left(1-a\right)\left(1-c\right)}}=2\sqrt{\dfrac{a}{1-c}\times\dfrac{c}{1-a}}\le\dfrac{a}{1-c}+\dfrac{c}{1-a}\)
Cộng vế với vế ta được :
\(2p\le\dfrac{a+c}{1-b}+\dfrac{b+c}{1-a}+\dfrac{a+b}{a-c}\)
\(\Leftrightarrow2p\le\dfrac{1-b}{1-b}+\dfrac{1-a}{1-a}+\dfrac{1-c}{1-c}\)
\(\Leftrightarrow2p\le3\)
\(\Leftrightarrow p\le\dfrac{3}{2}\)
Mặt khác a = b = c = \(\dfrac{1}{3}\) thì \(p=\dfrac{3}{2}\)
Vậy maxP = \(\dfrac{3}{2}\)
HỦY DIỆT THE WORLD selected this answer. -
Nguyễn Thị Thanh Hiền 04/12/2017 at 07:52
p = √one b( 1 - a ) ( 1 - b ) +√b c( 1 - b ) ( 1 - c ) +√một c( 1 - a ) ( 1 - c )
Theo Bất Đẳng Thức Cosi ta có:
2 √one b( 1 - a ) ( 1 - b ) =2√một1 - b ×b1 - a ≤a1 - b +b1 - a
2 √b c( 1 - b ) ( 1 - c ) =2√b1 - c ×c1 - b ≤b1 - c +c1 - b
2 √một c( 1 - a ) ( 1 - c ) =2√một1 - c ×c1 - a ≤a1 - c +c1 - a
Cộng sản:
2 p ≤ a + c1 - b +b+c1 - a +a+ba - c
⇔ 2 p ≤ 1 - b1 - b +1-a1 - a +1-c1-c
⇔2p≤3
⇔p≤32
Mặt other a = b = c = 13 thì p=32
Then maxP = 32