Solving for the Unknown Sides

Oct 13, 2025 by wbrum.org 136 views

Introduction

In this problem, we are given a triangle with two known angles and the side opposite to the third angle. We need to find the lengths of the other two sides. This problem involves the use of trigonometry, specifically the Law of Sines, to solve for the unknown sides.

The Law of Sines

The Law of Sines is a fundamental concept in trigonometry that relates the lengths of the sides of a triangle to the sines of its angles. The Law of Sines states that for any triangle with angles A, B, and C, and sides a, b, and c opposite to those angles, respectively, the following equation holds:

a / sin(A) = b / sin(B) = c / sin(C)

Applying the Law of Sines

In this problem, we are given two angles, A = 31° and B = 68°, and the side c opposite to the third angle, which is 45 units long. We need to find the lengths of the other two sides, a and b. Using the Law of Sines, we can set up the following equations:

a / sin(A) = c / sin(C) b / sin(B) = c / sin(C)

Finding the Third Angle

To solve for the unknown sides, we need to find the measure of the third angle, C. We can use the fact that the sum of the angles in a triangle is always 180°. Therefore, we can set up the following equation:

A + B + C = 180° 31° + 68° + C = 180° C = 180° - 99° C = 81°

Solving for the Unknown Sides

Now that we have found the measure of the third angle, C, we can substitute this value into the equations we set up earlier:

a / sin(A) = c / sin(C) a / sin(31°) = 45 / sin(81°)

To solve for a, we can cross-multiply and simplify:

a = (45 * sin(31°)) / sin(81°)

Using a calculator to evaluate the trigonometric functions, we get:

a ≈ (45 * 0.5097) / 0.9786 a ≈ 23.5

Similarly, we can set up the following equation to solve for b:

b / sin(B) = c / sin(C) b / sin(68°) = 45 / sin(81°)

To solve for b, we can cross-multiply and simplify:

b = (45 * sin(68°)) / sin(81°)

Using a calculator to evaluate the trigonometric functions, we get:

b ≈ (45 * 0.9272) / 0.9786 b ≈ 42.2

Conclusion

In this problem, we used the Law of Sines to find the lengths of the other two sides of a triangle with two known angles and the side opposite to the third angle. We found that the lengths of the other two sides are approximately 23.5 and 42.2 units, respectively.

Answer

The correct answer is:

A. 24.8 is incorrect B. 42.2 is correct C. 81.6 is incorrect D. 23.5 is correct

Introduction

The Law of Sines

a / sin(A) = b / sin(B) = c / sin(C)

Applying the Law of Sines

a / sin(A) = c / sin(C) b / sin(B) = c / sin(C)

Finding the Third Angle

A + B + C = 180° 31° + 68° + C = 180° C = 180° - 99° C = 81°

Solving for the Unknown Sides

Now that we have found the measure of the third angle, C, we can substitute this value into the equations we set up earlier:

a / sin(A) = c / sin(C) a / sin(31°) = 45 / sin(81°)

To solve for a, we can cross-multiply and simplify:

a = (45 * sin(31°)) / sin(81°)

Using a calculator to evaluate the trigonometric functions, we get:

a ≈ (45 * 0.5097) / 0.9786 a ≈ 23.5

Similarly, we can set up the following equation to solve for b:

b / sin(B) = c / sin(C) b / sin(68°) = 45 / sin(81°)

To solve for b, we can cross-multiply and simplify:

b = (45 * sin(68°)) / sin(81°)

Using a calculator to evaluate the trigonometric functions, we get:

b ≈ (45 * 0.9272) / 0.9786 b ≈ 42.2

Conclusion

Q&A

Q: What is the Law of Sines?

A: The Law of Sines is a fundamental concept in trigonometry that relates the lengths of the sides of a triangle to the sines of its angles.

Q: How do we use the Law of Sines to solve for the unknown sides of a triangle?

A: We can use the Law of Sines to set up equations that relate the lengths of the sides to the sines of the angles. We can then solve for the unknown sides by cross-multiplying and simplifying the equations.

Q: What is the measure of the third angle in this problem?

A: The measure of the third angle, C, is 81°.

Q: How do we find the measure of the third angle?

A: We can use the fact that the sum of the angles in a triangle is always 180°. We can set up an equation using the given angles and solve for the third angle.

Q: What are the lengths of the other two sides of the triangle?

A: The lengths of the other two sides are approximately 23.5 and 42.2 units, respectively.

Q: What is the formula for the Law of Sines?

A: The formula for the Law of Sines is:

a / sin(A) = b / sin(B) = c / sin(C)

Q: Can we use the Law of Sines to solve for the unknown sides of any triangle?

A: Yes, we can use the Law of Sines to solve for the unknown sides of any triangle, as long as we have the measures of two angles and the length of the side opposite to the third angle.

Q: What is the significance of the Law of Sines in trigonometry?

A: The Law of Sines is a fundamental concept in trigonometry that allows us to relate the lengths of the sides of a triangle to the sines of its angles. It is a powerful tool for solving problems involving triangles and is used extensively in mathematics, physics, and engineering.

Answer

The correct answer is:

A. 24.8 is incorrect B. 42.2 is correct C. 81.6 is incorrect D. 23.5 is correct