Linear Approximation question

I'm currently having a hard time with this question:

Use differentials (or equivalently, a linear approximation) to approximate https://webwork.math.lsu.edu/webwork...19d16c3641.png as follows: Let https://webwork.math.lsu.edu/webwork...b31f9cbe11.png and find the equation of the tangent line to https://webwork.math.lsu.edu/webwork...910e13a9c1.png at a "nice" point near https://webwork.math.lsu.edu/webwork...efed1e2701.png. Then use this to approximate https://webwork.math.lsu.edu/webwork...19d16c3641.png.

I'm familiar with the linear approximation formula, but this is confusing me. I tried getting (with 29.1 as a "nice" point): (cos29.1)(x-29)(sin29.1) but that is incorrect. I think it has something to do with using this number and plugging it into the equation for a tangent line? I'm really not sure. Thanks in advance for any help!