回復 17# chiang 的帖子
第3題
\begin{align}
& {{\cos }^{2}}{{1}^{{}^\circ }}+{{\cos }^{2}}{{2}^{{}^\circ }}+{{\cos }^{2}}{{3}^{{}^\circ }}+\cdots +{{\cos }^{2}}{{179}^{{}^\circ }} \\
& =\left( {{\cos }^{2}}{{1}^{{}^\circ }}+{{\cos }^{2}}{{91}^{{}^\circ }} \right)+\left( {{\cos }^{2}}{{2}^{{}^\circ }}+{{\cos }^{2}}{{92}^{{}^\circ }} \right)+\cdots +\left( {{\cos }^{2}}{{89}^{{}^\circ }}+{{\cos }^{2}}{{179}^{{}^\circ }} \right) \\
& =89 \\
\end{align}
第4題
考古題,用"傾斜”在此站搜尋