**Quote:**

+4) + 6?

This is the method to get (

*a**x* +

*b*)² +

*c* type of a formula.

Here we have

*x*² – 4

*x* + 10. Knowing the formula of a square of a sum, (

*a* +

*b*)² =

*a*² + 2

*ab* +

*b*², we look at

*x*² – 4*x* and look at it as

*x*² – 2 × (2 ×

*x*). The missing

*b*² must be 2² = 4.

Therefore we represent

*x*² – 4

*x* + 10 as (

*x*² – 4

*x* + 4) + 6.