 If Xavier is twice as old as Yvonne and half the square of her age, how old is each? This is more complicated than the previous example in three respects: it has more unknowns, more equations, and terms of higher degree. We may take \(x\) for Xavier’s age and \(y\) for Yvonne’s age. The two constraints may be formalized as the equations \(x = 2y\) and \(x = y^2 /2\), the latter being of degree 2 or quadratic.