( )2 ( )X X X X X X X X4 2 2 1 2 2 8 8 2 2 2 1 22 2 4 2 22 + + = + +  + + = + + (X2 1)2 2(X 2)2 X2 1 2 X 2 + = +  + = +2 1 2 2 2 1 2

Bài 42: Giải phương trình : x

⁴

=8x+7 HD :

( )

²

( )

x x x x x x x x

4

2

2

1 2

2

8 8

2

2

2

1 2

2

2

4

2

2

2

 + + = + +  + + = + +

(

^x

²

¹

)

²

²

⁽

^{x 2}

⁾

²

^x

²

^{1 2 x 2} + = +  + = +

2

1 2 2

2

1 2. 2 2x x x x + = +  + = + x x − + = −x + = x+  −x x= −

²

2. 1 2 2 1

2

1 2. 2 2

2

2. 2 2 12 22

2

4 2 1x  − −  =