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Solving for a side in a right triangle using the trigonometric ratios

Solving for a side in a right triangle using the trigonometric ratios

In a right triangle, the trigonometric ratios—sine, cosine, and tangent—are used to relate the angles to the lengths of the sides. Here's a brief overview of each:

  1. Sine (sin): This ratio compares the length of the opposite side to the hypotenuse.

    sin(θ)=OppositeHypotenuse\sin(\theta) = \frac{\text{Opposite}}{\text{Hypotenuse}}
  2. Cosine (cos): This ratio compares the length of the adjacent side to the hypotenuse.

    cos(θ)=AdjacentHypotenuse\cos(\theta) = \frac{\text{Adjacent}}{\text{Hypotenuse}}
  3. Tangent (tan): This ratio compares the length of the opposite side to the adjacent side.

    tan(θ)=OppositeAdjacent\tan(\theta) = \frac{\text{Opposite}}{\text{Adjacent}}

To solve for a side of a triangle, you can rearrange these formulas based on the known values:

  • To find the length of the opposite side:

    Opposite=sin(θ)×HypotenuseorOpposite=tan(θ)×Adjacent\text{Opposite} = \sin(\theta) \times \text{Hypotenuse} \quad \text{or} \quad \text{Opposite} = \tan(\theta) \times \text{Adjacent}
  • To find the length of the adjacent side:

    Adjacent=cos(θ)×HypotenuseorAdjacent=Oppositetan(θ)\text{Adjacent} = \cos(\theta) \times \text{Hypotenuse} \quad \text{or} \quad \text{Adjacent} = \frac{\text{Opposite}}{\tan(\theta)}
  • To find the hypotenuse:

    Hypotenuse=Oppositesin(θ)orHypotenuse=Adjacentcos(θ)\text{Hypotenuse} = \frac{\text{Opposite}}{\sin(\theta)} \quad \text{or} \quad \text{Hypotenuse} = \frac{\text{Adjacent}}{\cos(\theta)}

By knowing one side length and one angle (other than the right angle), you can calculate the lengths of the other sides using these ratios.

Part 1: Solving for a side in right triangles with trigonometry

Sal is given a right triangle with an acute angle of 65° and a leg of 5 units, and he uses trigonometry to find the two missing sides.

When studying "Solving for a side in right triangles with trigonometry," focus on the following key points:

  1. Understand Right Triangle Basics:

    • A right triangle has one 90-degree angle.
    • The sides include the opposite side (opposite the angle of interest), the adjacent side (next to the angle), and the hypotenuse (the longest side).
  2. Know the Trigonometric Ratios:

    • Sine (sin): sin(θ) = opposite/hypotenuse
    • Cosine (cos): cos(θ) = adjacent/hypotenuse
    • Tangent (tan): tan(θ) = opposite/adjacent
  3. Using Inverse Trigonometric Functions:

    • To find an angle when two sides are known, use:
      • θ = sin⁻¹(opposite/hypotenuse)
      • θ = cos⁻¹(adjacent/hypotenuse)
      • θ = tan⁻¹(opposite/adjacent)
  4. Sketching and Labeling:

    • Always sketch the triangle and label the sides and angles beforehand to clarify which ratios to use.
  5. Solving for Unknown Sides:

    • Rearrange the trigonometric ratio equations to solve for the side you need.
    • For example:
      • To find the opposite side: opposite = hypotenuse × sin(θ)
      • To find the adjacent side: adjacent = hypotenuse × cos(θ)
  6. Calculating Angles and Side Lengths:

    • Use a calculator for trigonometric functions and ensure it's set to the correct mode (degrees or radians) as needed.
  7. Applications:

    • Apply these concepts to real-world problems involving heights, distances, and angles.

Understanding these points will enable you to effectively solve for unknown sides in right triangles using trigonometry.