Math Problem Statement

Using the Law of Sines to find a triangle with one obtuse angle if ∠A = 45°, a = 22, b = 25. Find ∠B, ∠C, and side c.

Solution

To solve this problem using the Law of Sines, let's go through the calculations step-by-step.

Step 1: Use the Law of Sines to Find ∠B

The Law of Sines states that: sinAa=sinBb=sinCc\frac{\sin A}{a} = \frac{\sin B}{b} = \frac{\sin C}{c}

Given:

  • A=45\angle A = 45^\circ
  • a=22a = 22
  • b=25b = 25

Substitute these values into the Law of Sines to find sinB\sin B: sin4522=sinB25\frac{\sin 45^\circ}{22} = \frac{\sin B}{25}

sinB=25sin4522\sin B = 25 \cdot \frac{\sin 45^\circ}{22}

Since sin45=22\sin 45^\circ = \frac{\sqrt{2}}{2}, we get: sinB=252/222=252440.801\sin B = 25 \cdot \frac{\sqrt{2}/2}{22} = \frac{25\sqrt{2}}{44} \approx 0.801

Taking the inverse sine, we find: Bsin1(0.801)53.1 or 126.9B \approx \sin^{-1}(0.801) \approx 53.1^\circ \text{ or } 126.9^\circ

Since we are asked for an obtuse angle, B=126.9\angle B = 126.9^\circ.

Step 2: Find ∠C

Using the fact that the sum of angles in a triangle is 180180^\circ: C=180AB=18045126.98.1C = 180^\circ - A - B = 180^\circ - 45^\circ - 126.9^\circ \approx 8.1^\circ

Step 3: Find Side cc

Using the Law of Sines again: sinAa=sinCc\frac{\sin A}{a} = \frac{\sin C}{c}

c=asinCsinA=22sin8.1sin45c = a \cdot \frac{\sin C}{\sin A} = 22 \cdot \frac{\sin 8.1^\circ}{\sin 45^\circ}

c220.1410.7074.39c \approx 22 \cdot \frac{0.141}{0.707} \approx 4.39

Final Answers

  • B126.9\angle B \approx 126.9^\circ
  • C8.1\angle C \approx 8.1^\circ
  • c4.39c \approx 4.39

Would you like further clarification on any of these steps?

  1. How would the solution change if B\angle B was acute instead?
  2. What if side bb were smaller than aa?
  3. How does the Law of Sines differ from the Law of Cosines?
  4. How is the obtuse angle determined in ambiguous SSA triangles?
  5. Why is the sum of angles in a triangle always 180180^\circ?

Tip: Always check for multiple angle solutions in SSA problems, as they may lead to ambiguous cases.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Law of Sines
Triangle Properties

Formulas

sin(A)/a = sin(B)/b = sin(C)/c
Sum of angles in a triangle = 180°

Theorems

Law of Sines
Angle Sum Property of a Triangle

Suitable Grade Level

Grades 10-12