`C=3x^2+5x+7`
`=> 3x^2+5x+\frac{25}{12}+\frac{59}{12} `
`=>3(x^2+\frac{5}{3}x+\frac{25}{36})+\frac{59}{12}`
`=3(x+\frac(5}{6})^2+\frac{59}{12}`
`Do`` (x+\frac(5}{6})^2\geq0`
`=>3(x+\frac(5}{6})^2+\frac{59}{12}\geq\frac{59}{12}>0`
`F=-x^2+2x-5`
`=-x^2+2x-1-4`
`=-(x^2-2x+1)-4`
`=-(x-1)^2-4`
`Do` `(x-1)^2\geq0`
`=>-(x-1)^2-4\leq-4<0`