Tính tổng/tích

The image contains a mathematical expression written in Vietnamese. The task is to calculate the sum or product of the given trigonometric terms. The expression is:

\[ M = \cos 10^\circ + \cos 30^\circ + \ldots + \cos 150^\circ + \cos 170^\circ \]

To calculate the sum of these cosine values, you can use the sum-to-product identities or numerical methods. However, the exact sum of these cosines is not straightforward to compute by hand due to the irregular intervals.

For a numerical approach, you can use a calculator or a programming tool to find the approximate sum:

\[ \cos 10^\circ + \cos 30^\circ + \cos 50^\circ + \cos 70^\circ + \cos 90^\circ + \cos 110^\circ + \cos 130^\circ + \cos 150^\circ + \cos 170^\circ \]

Using a calculator:

\[
\begin{align*}
\cos 10^\circ & \approx 0.9848 \\
\cos 30^\circ & \approx 0.8660 \\
\cos 50^\circ & \approx 0.6428 \\
\cos 70^\circ & \approx 0.3420 \\
\cos 90^\circ & = 0 \\
\cos 110^\circ & \approx -0.3420 \\
\cos 130^\circ & \approx -0.6428 \\
\cos 150^\circ & \approx -0.8660 \\
\cos 170^\circ & \approx -0.9848 \\
\end{align*}
\]

Adding these values together:

\[
0.9848 + 0.8660 + 0.6428 + 0.3420 + 0 - 0.3420 - 0.6428 - 0.8660 - 0.9848 = 0
\]

So, the sum \( M \) of these cosines is approximately 0.