Right Triangle - Unknown Side using Cosine

\[adjacent=hypotenuse\cos(\theta)\]

adjacent = length of the adjacent side (m)

hypotenuse = length of the hypotenuse (m)

theta = known angle of the right triangle (rad or °)

This trigonometric formula calculates the adjacent side of a right triangle using the cosine ratio.

The cosine function relates the adjacent side of an angle to the hypotenuse of the triangle.

It is one of the fundamental formulas used in trigonometry, geometry, engineering, and physics.

Use this formula when:

- The hypotenuse is known

- One acute angle is known

- The adjacent side must be calculated

- Solving right triangle problems

- Working with horizontal distances or vector components

The angle may be expressed in degrees or radians depending on the calculator configuration.

If:

hypotenuse = 15 m

theta = 35°

Then:

adjacent = 15*cos(35°)

adjacent ≈ 12.29 m

- Trigonometry and geometry

- Structural and civil engineering

- Physics and mechanics

- Navigation and surveying

- Vector analysis

- Computer graphics

Download the fCalc app to calculate this formula and thousands more:

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