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Ch. 1 - Angles and the Trigonometric Functions
Blitzer - Trigonometry 3rd Edition
Blitzer3rd EditionTrigonometryISBN: 9780137316601Non è quello che usi tu?Cambia libro di testo
Capitolo 1, Problema 1.3.73

In Exercises 61–86, use reference angles to find the exact value of each expression. Do not use a calculator. sin(-240°)

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Identify the given angle: \(-240^\circ\). Since it is negative, find its positive coterminal angle by adding \(360^\circ\): \(-240^\circ + 360^\circ = 120^\circ\).
Determine the reference angle for \(120^\circ\). Since \(120^\circ\) is in the second quadrant, the reference angle is \(180^\circ - 120^\circ = 60^\circ\).
Recall the sign of sine in the second quadrant. Sine is positive in the second quadrant, so \(\sin(120^\circ) = +\sin(60^\circ)\).
Use the exact value of \(\sin(60^\circ)\), which is \(\frac{\sqrt{3}}{2}\).
Therefore, \(\sin(-240^\circ) = \sin(120^\circ) = +\frac{\sqrt{3}}{2}\).

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