A particle starts executing simple harmonic motion from one extreme position. If \(\mathrm{a}, \mathrm{b}\) and \(c\) are the displacements of the particle from the mean position at the ends of three successive seconds, the frequency of simple harmonic motion is

1. A \(\frac{1}{\pi} \operatorname{Cos}^{-1}\left[\frac{\mathrm{a}+\mathrm{b}}{\mathrm{c}}\right]\)
2. B \(\frac{1}{2 \pi} \cos ^{-1}\left[\frac{b+c}{2 a}\right]\)
3. C \(\frac{1}{2 \pi} \operatorname{Cos}^{-1}\left[\frac{\mathrm{a}+\mathrm{c}}{2 \mathrm{~b}}\right]\)
4. D \(\frac{1}{2 \pi} \operatorname{Cos}^{-1}\left[\frac{\mathrm{a}+\mathrm{b}}{2 \mathrm{c}}\right]\)