When a, B, why is the value, the polynomial a to the second power + B to the second power + 2a-4b + 16 has the minimum value?

When a, B, why is the value, the polynomial a to the second power + B to the second power + 2a-4b + 16 has the minimum value?

a²+b²2a-4b+16
=﹙a²+2a+1﹚+﹙b²-4b+4﹚+11
=﹙a+1﹚²+﹙b-2﹚²+11
∵﹙a+1﹚²≥0,﹙b-2﹚²≥0
When a + 1 = 0, a = - 1
When B-2 = 0, B = 2
﹙a+1﹚²+﹙b-2﹚²+11≥11
The minimum value of this algebraic expression is 11