A = 4x⁴ + 7x²y² + 3y⁴ + 5y²

= 4x⁴ + 4x²y² + 3x²y² + 3y⁴ + 5y²

= 4x²(x² + y²) + 3y²(x² + y²) + 5y²

= 4x² . 5 + 3y² . 5 + 5y²

= 20x² + 15y² + 5y²

= 20x² + 20y²

= 20(x² + y²)

= 20 . 5 

= 100

 Thái Viết Nam 

Với x² + y² = 5

Ta có:

A = 4x⁴ + 7x² y²  + 3y⁴ + 5y²

    = 4x⁴  + 4x² y²  + 3x² y² + 5y² 

  = 4x² . ( x² + y² ) + 3y2 . ( x² + y² ) + 5y² 

= 4x²  . 5 + 3y²  . 5 + 5y² 

= 20x² + 15y²  + 5y²  

= 20x²  20y² = 20. ( x² + y² ) = 20 . 5 = 100

Vậy A = 100 

^^ Học tốt! 

A=4x⁴+7x²y²+3y⁴+5y²=(4x⁴+8x²y²+4y⁴)-x²y²-y⁴+5y²=(2x²+2y²)²-y²(x²+y²)+5y²=4(x²+y²)²-y²(x²+y²)+5y²

Thay x²+y²=5 vào A, Ta được:

A=4*5²-y²*5+5*y²=4*25=100

Vậy A=100

Bài 1:A=4x4+7x2y2+3y4+5y2=4x2(x2+y2)+3y2(x2+y2)+5y2=20x2+15y2+5y2=20(x2+y2)=100.

A=4x⁴+7x²y²+3y⁴+5y²

=4x²(x²+y²)+3y²(x²+y²)+5y²

=20x²+15y²+5y² 

=20x²+(15+5)y²

=20(x²+y²)=100

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minh cung k bit lam

A=4x⁴+7x²y²+3y⁴+5y⁵

=4x⁴+4x²y²+3x²y²+3y⁴+5y⁵

=4x²(x²+y²)+3y²(x²+y²)+5y²

=4x²5+3y²5+5y²

=20x²+15y²+5y²

=20x²+20y²

=20(x²+y²)

=20.5

=100

tại sao lại: 4x²(x²+y²)+3y²(x²+y²)+5y²

Với x2+y2=0x2+y2=0, ta có:

A=4x4+7x2y2+3y4+5y2

=4x4+4x2y2+3x2y2+3y4+5y2

=4x2.(x2+y2)+3y2.(x2+y2)+5y2

=4x2.5+3y2.5+5y2=20x2+15y2+5y2

=20x2+20y2=20.(x2+y2)=20.5=100

Vậy A=100

mình nhầm nhé

\(A=4x^4+8x^2y^2+4y^4-x^2y^2-y^4+5y^2\)

\(A=4\left(x^2+y^2\right)^2-y^2\left(x^2+y^2\right)+5y^2\)

\(A=4.5^2-y^2.5-5y^2\)

\(A=100\)