The gradient is a way of packing together all the partial derivative information of a function. So let’s just start by computing the partial derivatives of this guy. So partial of f with respect to x is equal to, so we look at this and we consider x the variable and y the constant. Well in that case sine of y is also a constant.

https://www.khanacademy.org/math/multivariable-calculus/multivariable-derivatives/gradient-and-directional-derivatives/v/gradient