Common Values of Sine, Cosine, & Tangent: Videos & Practice Problems

Trigonometric functions establish a relationship between angles and their corresponding points on the unit circle, where the x and y coordinates represent the cosine and sine values of those angles, respectively. To effectively solve trigonometric problems, it's essential to memorize the sine and cosine values for the three most common angles: 30°, 45°, and 60°. Two effective methods for memorization are the 1, 2, 3 rule and the left hand rule.

The 1, 2, 3 rule begins with the understanding that all sine and cosine values for these angles can be expressed as a fraction involving the square root of a number over 2. Starting with the angle of 60°, you count clockwise for the x values (cosine) and counterclockwise for the y values (sine). For example, the cosine of 60° is calculated as:

$$\cos(60°) = \frac{\sqrt{1}}{2} = \frac{1}{2}$$

Similarly, the sine of 30° is:

$$\sin(30°) = \frac{\sqrt{1}}{2} = \frac{1}{2}$$

To find the tangent of an angle, you can divide the sine by the cosine. For 30°, this results in:

$$\tan(30°) = \frac{\sin(30°)}{\cos(30°)} = \frac{\frac{1}{2}}{\frac{\sqrt{3}}{2}} = \frac{1}{\sqrt{3}} = \frac{\sqrt{3}}{3}$$

The left hand rule offers a more visual approach. By positioning your left hand in front of your face, with your pinky at 0° and your thumb at 90°, each finger represents a common angle: 30°, 45°, and 60°. To find the sine and cosine values, fold the finger corresponding to the angle you are interested in. For instance, for 30°, you would fold the finger representing 30° and count the fingers above and below it. The cosine of 30° is determined by the number of fingers above the folded finger:

$$\cos(30°) = \frac{\sqrt{3}}{2}$$

And the sine is determined by the fingers below:

$$\sin(30°) = \frac{\sqrt{1}}{2} = \frac{1}{2}$$

For tangent, you can again divide sine by cosine or count the fingers:

$$\tan(30°) = \frac{\sin(30°)}{\cos(30°)} = \frac{1}{\sqrt{3}} = \frac{\sqrt{3}}{3}$$

Both methods provide a solid foundation for memorizing trigonometric values and can be applied to any angle within the first quadrant. With practice, these techniques will enhance your ability to tackle a variety of trigonometric problems confidently.

Understanding the unit circle is essential for mastering trigonometry, particularly in the first quadrant where angles range from 0 to 90 degrees. The unit circle is a circle with a radius of 1, centered at the origin of a coordinate system. In this quadrant, we can identify key points and their corresponding angle measures in both degrees and radians.

Starting with the axes, at 0 degrees (or 0 radians), the coordinates are (1, 0), while at 90 degrees (or \(\frac{\pi}{2}\) radians), the coordinates are (0, 1). The angles of 30 degrees, 45 degrees, and 60 degrees are also significant. The radian measures for these angles can be derived as follows:

• For 30 degrees, which is \(\frac{1}{3}\) of 90 degrees, the radian measure is \(\frac{\pi}{6}\).
• For 45 degrees, being halfway between 0 and 90 degrees, the radian measure is \(\frac{\pi}{4}\).
• For 60 degrees, which is double 30 degrees, the radian measure is \(\frac{\pi}{3}\).

Next, we can determine the sine and cosine values for these angles, which correspond to the y and x coordinates, respectively. The sine and cosine values for the angles in the first quadrant can be expressed using the square root method:

• For 30 degrees: \(\sin(30^\circ) = \frac{1}{2}\) and \(\cos(30^\circ) = \frac{\sqrt{3}}{2}\).
• For 45 degrees: \(\sin(45^\circ) = \cos(45^\circ) = \frac{\sqrt{2}}{2}\).
• For 60 degrees: \(\sin(60^\circ) = \frac{\sqrt{3}}{2}\) and \(\cos(60^\circ) = \frac{1}{2}\).

To find the tangent values, we use the relationship that tangent is the ratio of sine to cosine, or \( \tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)} \). This gives us:

• For 30 degrees: \(\tan(30^\circ) = \frac{\frac{1}{2}}{\frac{\sqrt{3}}{2}} = \frac{1}{\sqrt{3}} \approx \frac{\sqrt{3}}{3}\) after rationalizing the denominator.
• For 45 degrees: \(\tan(45^\circ) = \frac{\frac{\sqrt{2}}{2}}{\frac{\sqrt{2}}{2}} = 1\).
• For 60 degrees: \(\tan(60^\circ) = \frac{\frac{\sqrt{3}}{2}}{\frac{1}{2}} = \sqrt{3}\).

Additionally, at the axes, we have:

• At 0 degrees: \(\tan(0^\circ) = \frac{0}{1} = 0\).
• At 90 degrees: \(\tan(90^\circ) = \frac{1}{0}\), which is undefined.

By practicing these values and their relationships, you can become proficient in using the unit circle for trigonometric calculations. Repetition and familiarity with these key points will enhance your understanding and ability to apply trigonometric concepts effectively.