Find derivatives of sine and cosine functions

Exercise 11. Given a function f:R2R f: \mathbb{R}^{2} \rightarrow \mathbb{R} , the first-order partial derivatives are provided:\newlinefx(x,y)=6x6y and fy(x,y)=6y26x. \frac{\partial f}{\partial x}(x, y)=6 x-6 y \quad \text { and } \quad \frac{\partial f}{\partial y}(x, y)=6 y^{2}-6 x . \newline(a) Determine all stationary points of f f .\newline(b) Compute the second-order partial derivatives of f f and find the Hessian matrix Hf(x,y) \boldsymbol{H}_{f}(x, y) of f f . Determine the points in the (x,y) (x, y) plane where f f has a local maximum, a local minimum or a saddle point.\newline(c) It is now stated that f(0,0)=1 f(0,0)=1 . Determine the second-degree Taylor polynomial P2(x,y) P_{2}(x, y) for f f with the expansion point f f 00.\newlineExercise 22. Define the function f f 11 by\newlinef(x)={sin(x)xx0,1x=0. f(x)=\left\{\begin{array}{ll} \frac{\sin (x)}{x} & x \neq 0, \\ 1 & x=0 . \end{array}\right. \newline(a) Find the third-degree Taylor polynomial f f 22 of f f 33 with expansion point f f 44.\newline(b) Show that\newlinelimx0sin(x)x=1. \lim _{x \rightarrow 0} \frac{\sin (x)}{x}=1 . \newlineHint: Use (a) and Taylor's limit formula.\newline(c) Argue that f f is continuous on f f 66.\newline(d) Compute, e.g. using SymPy, a decimal approximation of f f 77. You should include at least 55 decimals.\newline(e) Compute a Riemann sum f f 88 approximating f f 77, where we require that f f 00 for each f f 11.
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