Answer:
Therefore the critical point is (x,y)=
.
Therefore
is local minimum.
Step-by-step explanation:
Given function is

The partial derivatives of z are

and

To find the critical point, setting the partial derivatives equal to zero.
∴16x+2y+5 =0......(1) and 2x+2y+1=0.......(2)
Now solving the above equation,
Subtract equation (2) from equation (1)
16x+2y+5-( 2x+2y+1)=0
⇒16x+2y+5-2x-2y-1=0
⇒8x+4=0
⇒ 8x = -4


Now putting the value of x in (2)


⇒2y=0
⇒y=0
Therefore the critical point is (x,y)=
.
Second order partial derivatives are
,
and 
The discriminant


=14>0
D
= 14 >0, Then at
is either local minimum or local maximum.
Since
, So the function is concave up.
Therefore
is local minimum.