By completing the square: x²-8x+19 = (x-4)²-16+19 = (x-4)²+3 so minimum point = (4,3)
By calculus: f'(x) = 2x-8. (minimum point occurs when f'(x)=0 therefore)
2x-8 = 0 means x=4 and the corresponding y value is 3.
The minimum value of this function (y) is 3 and this occurs when x = 4.
