Menu

English

The Opposite Side

Part of the Right-Triangle Trigonometry section of Coddy's Trigonometry journey. Lesson 3 of 50.

The other two sides are named from one of the two acute angles, the angles under 90°. Call that angle θ, the Greek letter theta. The side opposite θ is the one across the triangle from it: it does not touch θ at all.

$Right triangle ABC, θ at A, the side BC opposite θ$

Here θ sits at A. Its two arms run along AB and AC, so the side across from it is BC. A quick test: put a finger on θ and slide it straight across the inside of the triangle. The side you hit is the opposite side.

Challenge

Triangle KLM has a right angle at M, and θ is at K. Tap the side opposite θ. Then press Check.

Try it yourself

$Find the right part on the figure$

Find the right part on the figure

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Right-Triangle Trigonometry

1Sides of a Right Triangle

How Tall Is the Tree?The HypotenuseThe Opposite SideThe Adjacent Side When the Angle Moves Recap: Naming the Sides

4Finding the Hypotenuse

The Unknown Below the Bar How Long Is the Kite String?A Leg Below the Bar Is the Answer Sensible?Recap: The Hypotenuse

7Elevation and Depression

Angle of Elevation Measuring From Eye Level Angle of Depression The Sun's Angle Two Triangles, One Height Recap: Looking Up and Down

2The Three Ratios

The Sine Ratio The Cosine Ratio The Tangent Ratio Choosing the Ratio Recap: The Three Ratios

5Finding an Angle

Inverse Sine Inverse Cosine Inverse Tangent The Angle of a Ramp Both Acute Angles Recap: Finding an Angle

8Reciprocal Ratios

Cosecant, Secant, Cotangent Exact Reciprocal Values A Side From a Cosecant A Ladder and a Secant Recap: Reciprocal Ratios

3Finding a Side

Sides at Any Angle Rounding the Answer Tangent: Leg From Leg A Ladder Against a Wall The Other Acute Angle Recap: Finding a Side

6Special Triangles, Exactly

The Two Special Triangles An Exact Hypotenuse The Side Next to 30°An Exact Angle Recap: Exact Values

9Final Challenges

Is the Ladder Safe?The Wheelchair Ramp Two Observers The Landing Plane The Kite The Sun's Angle, Exactly