二元函数 最小值点$(\frac{1}{6}(3-2 \pi),\frac{1}{6}(-3-2 \pi))$

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证明McCormick函数${\displaystyle f(x,y)=\sin \left(x+y\right)+\left(x-y\right)^{2}-1.5x+2.5y+1}$的最小值点为
\[
\begin{array}{ll}
(\frac{1}{6}(3-2 \pi)+2k\pi, \frac{1}{6}(-3-2 \pi)+2k\pi)\\
(\frac{1}{6}(3+2 \pi)+2k\pi, \frac{1}{6}(2 \pi-3)+2k\pi)\\
\end{array}
\]