Question

[linhlucy]

2 giây trước (20:21)

1.Viết các biểu thức sau dưới dạng tích :

54, \(25x^2y^4+30xy^2z+9z^2\)

55, \(\dfrac{16}{9}x^2+4xyz^2+\dfrac{9}{4}y^2z^4\)

2. Tính gt bt sau :

56, \(\dfrac{9}{25}x^2+\dfrac{12}{35}xy+\dfrac{4}{49}y^2\) tại x=5, y=-7

57, \(\dfrac{25}{16}u^4v^2+\dfrac{1}{5}u^2v^3+\dfrac{4}{625}v^4\) tại u= \(\dfrac{2}{5}\) , v= -5

Answer 1

[Mashiro Shiina]

1)\(25x^2y^4+30xy^2z+9z^2=\left(5xy^2+3z\right)^2\)

\(\dfrac{16}{9}x^2+4xyz^2+\dfrac{9}{4}y^2z^4=\left(\dfrac{4}{3}x+\dfrac{3}{2}yz^2\right)^2\)

2)

a)\(\dfrac{9}{25}x^2+\dfrac{12}{35}xy+\dfrac{4}{49}y^2=\left(\dfrac{3}{5}x+\dfrac{2}{7}y\right)^2=\left(\dfrac{3}{5}.5+\dfrac{2}{7}.\left(-7\right)\right)^2=\left(3-2\right)^2=1\)b)\(\dfrac{25}{16}u^4v^2+\dfrac{1}{5}u^2v^3+\dfrac{4}{625}v^4\)

\(=\left(\dfrac{5}{4}u^2v+\dfrac{2}{25}v^2\right)^2=\left(\dfrac{5}{4}.\dfrac{4}{25}.\left(-5\right)+\dfrac{2}{25}.\left(-5\right)^2\right)^2\)

\(=\left(-1+2\right)^2=1\)