Secant of 240 Degrees
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Theorem
- $\sec 240 \degrees = \sec \dfrac {4 \pi} 3 = - 2$
where $\sec$ denotes secant.
Proof
| \(\ds \sec 240 \degrees\) | \(=\) | \(\ds \map \sec {360 \degrees - 120 \degrees}\) | ||||||||||||
| \(\ds \) | \(=\) | \(\ds \sec 120 \degrees\) | Secant of Conjugate Angle | |||||||||||
| \(\ds \) | \(=\) | \(\ds -2\) | Secant of $120 \degrees$ |
$\blacksquare$
Sources
- 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 5$: Trigonometric Functions: Exact Values for Trigonometric Functions of Various Angles