Plotting a graph takes time. Often mathematicians just want to know the key features. These are: shape, location and some key points (such as where the graph crosses the axes or turning points).

work out \(y\) when \(x = 0\): \(0^2 – 6 \times 0 + 9 = 9\) so the graph crosses the \(y\)-axis at \(y = 9\). Sketching a quadratic using the turning point and the line of symmetry - Higher The ...