"gradf" stands for the gradient of the function f. It is a vector that represents the direction and magnitude of the steepest increase of the function at a given point.
The variables in this equation are x and y. They are independent variables that determine the value of the function f. In this case, x and y are used to calculate the gradient of f.
The "i" and "j" represent the unit vectors in the x and y directions, respectively. They are used to indicate the direction of the gradient vector in the x and y directions.
The sine function is used to calculate the component of the gradient vector in the x direction. It is a trigonometric function that relates the angle and side lengths of a right triangle.
This equation cannot be directly solved for f because it is a gradient vector equation. Instead, it can be used to calculate the gradient of f at a specific point (x,y). To solve for f, the equation would need to be rearranged and integrated, assuming f is a function of x and y.