Question

Answer 1

c: Để \(A=\dfrac{2}{6-x}\) max thì 6-x=1

=>x=5

d: \(3x^4+5x^2y^2+2y^4+2y^2+2009\)

\(=3x^4+3x^2y^2+2x^2y^2+2y^4+2y^2+2009\)

\(=\left(x^2+y^2\right)\left(3x^2+2y^2\right)+2y^2+2009\)

\(=6x^2+4y^2+2y^2+2009\)

\(=6x^2+6y^2+2009\)

\(=6\left(x^2+y^2\right)+2009\)

\(=6\cdot2+2009=2021\)