This is Section 6.2 Problem 18:For the function f(x,y)=x2y2+4x+6y+2, do the following:(a) Determine its critical point(s) if exists. Express your answer as coordinate pairs with parentheses and commas. Separate your answers with commas and list in ascending order of x if the function has more than one critical point. Use ``DNE'' if the function has no critical point.Answer: (b) Use the D-Test to classify at each critical point whether the function has a relative maximum or minimum, or a saddle point, or inconclusive:At the critical point, the D value is ---Select--- zero negative positive , and the second order partial derivative fxx is ---Select--- positive zero negative . Therefore at this point ---Select--- the D-Test has no conclusion the function has a relative minimum the function has a saddle point the function has a relative maximum .