là mày hả

a) \(x^2-6x-y^2-4y+5=x^2-6x+9-y^2-4y-4\)

\(=\left(x^2-6x+9\right)-\left(y^2+4y+4\right)=\left(x-3\right)^2-\left(y+2\right)^2\)

b) \(4a^2-12a-b^2+2b+8=4a^2-12a+9-b^2+2b-1\)

\(=\left(4a^2-12a+9\right)-\left(b^2-2b+1\right)=\left(2a-3\right)^2-\left(b-1\right)^2\)

x² - 6x - y² - 4y + 5

= ( x² - 6x + 9 ) - ( y² + 4y + 4 )

= ( x - 3 )² - ( y + 2 )²

4a² - 12a - b² + 2b + 8

= ( 4a² - 12a + 9 ) - ( b² - 2b + 1 )

= ( 2a - 3 )² - ( b - 1 )²

a) \(3x-3+5\left(1-x\right)\)

   \(=3x-3+5-5x\)

   \(=3x-5x+2\)

   \(=x\left(3-5\right)+2\)

   \(=-2x+2\)

    \(=2\left(1-x\right)\)

b) \(12a^2-3ab+8ac-2bc\)

  \(=3a\left(4a-b\right)+2c\left(4a-b\right)\)

  \(=\left(4a-b\right)\left(3a+2c\right)\)

c) \(x^2-25+y^2-2xy\)

   \(=x^2-2xy+y^2-25\)

   \(=\left(x-y\right)^2-5^2\)

   \(=\left(x-y-5\right)\left(x-y+5\right)\)

a) \(-5x-10xy-15y=-5\left(x+2xy+3y\right) \)

b) \(3a^2x-ba^2y+12a=a\left(3ax-bay+12\right) \)

c) \(2\left(x-y\right)-a\left(y-x\right)=\left(2+a\right)\left(x-y\right) \)

d) \(3a\left(x-y\right)-a^2\left(y-x\right)=\left(3a+a^2\right)\left(x-y\right) \)

Ta có A = 12   –   ( 2 a   –   3 ) 2   ≤   12 ∀ a  Þ A_max = 12 Û a = 3 2 .