BDAHABAC= CEHEDBPDPA HD QE

1,5QA= AB .BDAHABAC= CEHEDBPDPA HD QE. . 1�PD HE QA =0,5AH, DQ, EP đ ng quy (Đ nh lí Ceva)ồ ị1a) 2 đi mể

3

f x x 2x 3x ... nx 3

(6 đi m)

ể

Xét 

n

( )

²

³

ⁿ

= + + + + − 4        

          f x

n

^'

( ) = + 1 2 x 3 x

²

+

^{2 2}

+ + ... n .x

²

^{n 1}

⁻

Ta có  f x

n

^'

( ) > ∀ 0  x R f x  đ ng bi n, liên t c  trên R. 

n

( ) ồ ế ụ

Mà  f 0

n

( ) < 0; f 1

n

( ) > 0

( )

�  có nghi m duy nh t và nghi m đó thu c  ệ ấ ệ ộ ( ) ^0;1

f x

n

= 0

b) 4 đi m ể

−

2

n 1

1 1 1 1 9

� � = + + � � + + � � −

3f 1 2. 3 ... n

� � � � � �

3 3 3 3 4

 

2

n 1

n

1 1 1 1 1 3

� � = + � � + + − � � + � � −

f 2 ... n 1 n

� � � � � � � �

3 3 3 3 3 4

−

+

1 1 1 1 n 3 3 2n

� � = + + � � + + � � − − = −

2f 1 ...

� � � � � � �

n

n

3 3 3 3 3 2 2.3

� � = − + < ∀

1 2n 3

*

f 0  n N

� � � �