Math Problem Statement

Consider a triangle ABC like the one below. Suppose that b = 25, a = 31, and B = 34°. Solve the triangle.

Solution

To solve this triangle, we’ll use the Law of Sines because we have two sides and a non-included angle (SSA case). Here's the solution process:

Given:

  • a=31a = 31
  • b=25b = 25
  • B=34B = 34^\circ

Step 1: Find Angle AA Using the Law of Sines

The Law of Sines states: sinAa=sinBb\frac{\sin A}{a} = \frac{\sin B}{b} Substitute the values: sinA31=sin3425\frac{\sin A}{31} = \frac{\sin 34^\circ}{25}

Calculate sin34\sin 34^\circ (rounded to four decimal places): sin340.5592\sin 34^\circ \approx 0.5592 So: sinA31=0.559225\frac{\sin A}{31} = \frac{0.5592}{25}

Solving for sinA\sin A: sinA=31×0.5592250.6932\sin A = \frac{31 \times 0.5592}{25} \approx 0.6932

Now, we calculate AA: A=arcsin(0.6932)43.9A = \arcsin(0.6932) \approx 43.9^\circ

Step 2: Determine if There's a Second Possible Solution for AA

In an SSA case, there could be two possible triangles (the ambiguous case). We also check for: A=18043.9136.1A' = 180^\circ - 43.9^\circ \approx 136.1^\circ

If AA' were true, then A+B=136.1+34=170.1A' + B = 136.1^\circ + 34^\circ = 170.1^\circ, which is possible in a triangle (sum < 180°). Therefore, we have two possible solutions for AA.

Step 3: Calculate Angle CC for Each Case

  1. First Solution: A=43.9A = 43.9^\circ C=180AB=18043.934=102.1C = 180^\circ - A - B = 180^\circ - 43.9^\circ - 34^\circ = 102.1^\circ

  2. Second Solution: A=136.1A' = 136.1^\circ C=180AB=180136.134=9.9C' = 180^\circ - A' - B = 180^\circ - 136.1^\circ - 34^\circ = 9.9^\circ

Step 4: Find Side cc Using the Law of Sines

For each case:

  1. First Solution: csinC=asinAc=31sin102.1sin43.9\frac{c}{\sin C} = \frac{a}{\sin A} \Rightarrow c = \frac{31 \cdot \sin 102.1^\circ}{\sin 43.9^\circ} Calculate sin102.10.974\sin 102.1^\circ \approx 0.974 and sin43.90.6941\sin 43.9^\circ \approx 0.6941: c310.9740.694143.5c \approx \frac{31 \cdot 0.974}{0.6941} \approx 43.5

  2. Second Solution: c=31sin9.9sin136.1c' = \frac{31 \cdot \sin 9.9^\circ}{\sin 136.1^\circ} Calculate sin9.90.172\sin 9.9^\circ \approx 0.172 and sin136.10.6941\sin 136.1^\circ \approx 0.6941: c310.1720.69417.7c' \approx \frac{31 \cdot 0.172}{0.6941} \approx 7.7

Summary of Solutions

  1. First Solution:

    • A43.9A \approx 43.9^\circ
    • C102.1C \approx 102.1^\circ
    • c43.5c \approx 43.5
  2. Second Solution:

    • A136.1A' \approx 136.1^\circ
    • C9.9C' \approx 9.9^\circ
    • c7.7c' \approx 7.7

Would you like any further details on this solution, or have any questions?


Related Questions:

  1. How can we apply the Law of Cosines in a similar SSA scenario?
  2. What conditions determine whether a triangle has no solution in SSA cases?
  3. How would the solution change if angle BB were larger than 90 degrees?
  4. Can you have multiple solutions for a triangle in other configurations besides SSA?
  5. What other methods exist for solving non-right triangles?

Tip:

In SSA cases, always check for the ambiguous case to see if two solutions are possible.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Law of Sines
Ambiguous Case (SSA)

Formulas

Law of Sines: sin(A)/a = sin(B)/b = sin(C)/c

Theorems

Law of Sines

Suitable Grade Level

Grades 10-12