Final answer:
To find the angle theta when given the partial derivatives fx and fy, you can use the arctangent function tan^-1(fy/fx).
Step-by-step explanation:
To find the angle theta when given the partial derivatives fx and fy, you can use the arctangent function. The formula is theta = tan-1(fy/fx). This formula allows you to find the angle between the positive x-axis and the vector defined by fx and fy. You can use this method in calculus to find the direction of steepest ascent or descent at a particular point.