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Ch. 7 - Applications of Trigonometry and Vectors
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161Not the one you use?Change textbook
Chapter 8, Problem 58

Find the area of each triangle ABC.


A = 59.80°, b = 15.00 cm, C = 53.10°

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1
Identify the given elements of the triangle: angle A = 59.80°, side b = 15.00 cm, and angle C = 53.10°.
Calculate the third angle B using the triangle angle sum property: \(B = 180^\circ - A - C\).
Use the Law of Sines to find side a, which is opposite angle A: \(\frac{a}{\sin A} = \frac{b}{\sin B}\), so \(a = b \times \frac{\sin A}{\sin B}\).
Calculate the height (altitude) of the triangle relative to base b using the formula \(h = a \times \sin C\).
Find the area of the triangle using the formula \(\text{Area} = \frac{1}{2} \times b \times h\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Law of Sines

The Law of Sines relates the sides and angles of a triangle, stating that the ratio of a side length to the sine of its opposite angle is constant. It is useful for finding unknown sides or angles when given two angles and one side, as in this problem.
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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 angle, which is essential for applying trigonometric formulas correctly.
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Sum and Difference of Tangent

Area Formula Using Two Sides and Included Angle

The area of a triangle can be calculated using the formula (1/2)ab sin(C), where a and b are two sides and C is the included angle between them. This formula is especially useful when two sides and the included angle are known or can be found.
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Calculating Area of ASA Triangles