Bài `1`
` 3x^2 -5x +7 = 3(x^2 -5/3 x) +7 = 3(x^2 -2*5/6x + 25/36) - 3* 25/36 +7 = 3( x -5/6)^2 + 59/12 \ge 59/12`
` => A_(min) = 59/12` khi ` x -5/6 = 0 => x= 5/6`
Bài `2`
` \to C = (2(9x^2 - 24x + 21) +10)/(9x^2 -24x+21) = 2 +10/(9x^2 -24x +21)`
` C(max)` khi ` 10/(9x^2 -24x+21)` max `=> 9x^2 -24x + 21` min
` => 9(x^2 + 8/3x) +21` min
` => 9(x^2 +2*8/6x + 64/36) - 9*64/36 +21` min
`=> 9( x +8/6)^2 +5` min
` => x =-8/6`
` => C = 2 + 10/5 = 4`
` => C_(max) = 4`
