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Ch. 7 - Applications of Trigonometry and Vectors
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 3

Use the law of sines to find the indicated part of each triangle ABC.


Find B if C = 51.3°, c = 68.3 m, b = 58.2 m

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Identify the known parts of the triangle: angle \(C = 51.3^\circ\), side \(c = 68.3\) m (opposite angle \(C\)), and side \(b = 58.2\) m (opposite angle \(B\)). We need to find angle \(B\).
Recall the Law of Sines formula: \(\frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C}\). We will use the relationship between sides \(b\), \(c\) and angles \(B\), \(C\).
Set up the equation using the Law of Sines for sides \(b\) and \(c\): \(\frac{b}{\sin B} = \frac{c}{\sin C}\). Substitute the known values: \(\frac{58.2}{\sin B} = \frac{68.3}{\sin 51.3^\circ}\).
Solve for \(\sin B\) by cross-multiplying: \(\sin B = \frac{58.2 \times \sin 51.3^\circ}{68.3}\). Calculate the right side to find \(\sin B\) (do not compute the final value here).
Find angle \(B\) by taking the inverse sine (arcsin) of the value obtained for \(\sin B\): \(B = \sin^{-1}(\sin B)\). Remember to consider the possible ambiguous case for angle \(B\) in the triangle.

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Law of Sines

The Law of Sines relates the ratios of the lengths of sides of a triangle to the sines of their opposite angles. It states that (a/sin A) = (b/sin B) = (c/sin C). This law is useful for solving triangles when given two angles and one side or two sides and a non-included angle.
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Intro to Law of Sines

Triangle Angle Sum Property

The sum of the interior angles in any triangle is always 180°. Knowing two angles allows you to find the third by subtracting their sum from 180°. This property helps verify or find missing angles after applying the Law of Sines.
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Sum and Difference of Tangent

Solving for an Unknown Angle

When two sides and an angle opposite one of them are known, the Law of Sines can be used to find an unknown angle by rearranging the formula and using inverse sine functions. Care must be taken to consider the ambiguous case where two different angles may satisfy the equation.
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Solving Problems with Complementary & Supplementary Angles