From Tim Jackson
I was dismayed to see that Â鶹´«Ã½ has dumbed down to the extent of needing an analogy for the graph of a quadratic equation in Stephen Ornes’s article on playing pool (8 May, p 34).
He could at least have picked something the right shape. Lest we forget, a rainbow is an arc of a circle centred on the shadow of the viewer’s head, and has the same curvature all the way around. The graph of a quadratic function is a parabola, the curvature of which reduces progressively along its legs.
Haslingden, Lancashire, UK
