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In the displayed Fourier-series setup, $a_1$ is the coefficient for $\cos(t)$, which corresponds to the base frequency of $\frac{1}{2\pi}$ hertz. $a_2$ is the coefficient for $\cos(2t)$, corresponding to $\frac{1}{\pi}$ hertz.

Conditions: The function is represented in the displayed form with cosine coefficients $a_1, a_2, a_3$.; The comparison is about the coefficients multiplying $\cos(t)$ and $\cos(2t)$.

In the displayed Fourier-series setup, $a_1$ is the coefficient for $\cos(t)$, which corresponds to the base frequency of $\frac{1}{2\pi}$ hertz. $a_2$ is the coefficient for $\cos(2t)$, corresponding to $\frac{1}{\pi}$ hertz.

Conditions: The function is represented in the displayed form with cosine coefficients $a_1, a_2, a_3$.; The comparison is about the coefficients multiplying $\cos(t)$ and $\cos(2t)$.