A + B + C + 2  4(A2B2 C2 4)4 1 4( ) 2A B C A B CA C B C...

Câu 6. a + b + c + 2  4(a

²

b

²

 c

²

4)4 1 4( )

2

a b c a b ca c b c  a b         = 2(a + b+c)

²

( 2 )( 2 ) (3 3 ).3(a+b). 2 2 2  Vậy 8 27

₂

Pa b c  a b cP g t     . Đặt t = a + b + c, t > 0; ^{8 27}

₂

( )2 2( )2 2t t g’(t) = 8

₂

27

₃

(t 2) tg’(t) = 0  27(t + 2)

²

– 8t

³

= 0  t = 6 t 0 6 + g’(t) + 0 - g(t) ⁵8P  g(t)  58 xảy ra khi a = b = c = 2. 8; maxP = 5

B

C