81.42X2−3X+1−78.62X2−3X+1+16.92X2−3X+1 ≤0 ( )1GIẢI

Bài 1.

^81.4

²

^x

²

⁻

³

^x

⁺

¹

^−78.6

²

^x

²

⁻

³

^x

⁺

¹

^+16.9

²

^x

²

⁻

³

^x

⁺

¹

^≤0

( )

¹

Giải:

( )

2

2

x

−

x

+

x

−

x

+

x

−

x

+

x

−

x

+

2

3

1

2. 2

3

1

2

3

1

2

3

1

   6 93 3

( )

⇔ −   +   ≤81 78 16 01 81 78 16 0   4 42 2

2

2

3

1

−

+

x

x

=  3t

Đặt

 

Đk: t>0

22 8;t  ⇔ ∈ 

Phương trình trở thành:

16t

²

−78t+81 0≤ 3 27⇔ ≤   ≤ ⇔ ≤ − + ≤3 3 27

2

1 2 3 1 3x x 2 2 8

32

 ≥x ≥ − + ≥  − ≥  ≤2 3 1 1 2 3 0 0x x x x x  ⇔ ≤  ⇔ ⇔1 2 3 1 3 2 3 2 0 1   ≤− + ≤ − − ≤ x x x x ≥