when sketching a quadratic, instead of completing the square he suggests factorising the non-constant terms to easily find two values with the same y-ordinate:

x = 0 or 5 both give y-values of 3

so the curve must be symmetrical about a vertical line mid-way between these x values (x = 2.5), enabling the lowest point (vertex) of the quadratic to be calculated

this lowest point (vertex) can also be located by considering the lowest point of y = x(x - 5) and then translating this 3 spaces up

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