96.30 Quadratic doublets

摘要

I have known for some time that x~2 + 17x + 30 is a convenient example when teaching quadratics, because it is a monic quadratic(one in which the coefficient of x~2 is 1)that factorises but can quickly be turned into a non-monic quadratic that also factorises, simply by changing the coefficient of x~2 from 1 to 2