0\; \to \; A=2\cdot (-\frac{1}{\sqrt5})^2+\frac{1}{2\cdot (-1/\sqrt5)\cdot (2/\sqrt5)}=\\\\=10-\frac{5}{4}=\frac{2}{5}-\frac{5}{4}=-\frac{17}{20}" alt="b)\; \; \frac{3\pi }{2}0\; \to \; A=2\cdot (-\frac{1}{\sqrt5})^2+\frac{1}{2\cdot (-1/\sqrt5)\cdot (2/\sqrt5)}=\\\\=10-\frac{5}{4}=\frac{2}{5}-\frac{5}{4}=-\frac{17}{20}" align="absmiddle" class="latex-formula">