Explanation:

ensing that the denominator must be a factor of the numerator by noticing the nature of the choice values, we resort straightaway to algebraic manipulation of isolating the factor a²−bc in the numerator of the target expression.
Thus at the first step we get, numerator,
N=a²−bc+(b+c)²−bc
=a²−bc+(−a)²−bc
=a²−bc+a²−bc
=2(a²−bc)
With denominator (a²−bc) cancelling out against the numerator,
Target expression, E=2.