It is proved that the square of - x + 6x_ The constant value of 10 is less than zero

It is proved that the square of - x + 6x_ The constant value of 10 is less than zero

-x^2+6x-10=-(x^2-6x+10)=-(x^2-6x+9+1)=-(x-3)^2-1
The answer is obvious