Use Special Triangles to Determine Trigonometric Functions: CCSS.Math.Content.HSF-TF.A.3 - Common Core: High School - Functions

Card 1 of 48

1 of 2019 left
0 Learning0 Mastered

Calculate sine of the following angle.

Tap to see back

This question tests one's ability to understand the connection between special triangles (30-60-90 and 45-45-90), trigonometric functions related to them (sine, cosine, tangent), and the corresponding degree/radian on the unit circle. It relies on the understanding that the measure of an angle can be described using the properties of the unit circle and arc length. Furthermore, questions involving concepts dealing with trigonometry use the foundation of corresponding identities with angles that come from the unit circle. Recall that the unit circle is a circle that has a radius of one and is centered at the origin. Each pair that lies on the circle can be found by creating a right triangle that has a base on the -axis and a hypotenuse that is from the center of the circle to the desired point on the edge of the circle. The height of the triangle is the vertical line that connects the point on the circle's edge to the -axis.

For the purpose of Common Core Standards, understanding "use special triangles to determine geometrically the values of sine, cosine, tangent for " , falls within the Cluster A of "extend the domain of trigonometric functions using the unit circle" concept (CCSS.MATH.CONTENT.HSF.TF.A).

Knowing the standard and the concept for which it relates to, we can now do the step-by-step process to solve the problem in question.

Possible approaches to solving this problem:

I. Plot the angle on the unit circle to find the .

II. Identify the special triangle that corresponds to the angle.

III. Using memorization of the unit circle.

For this particular question let's us approach II.

Step 1: Simplify the angle if possible.

Step 2: Identify the special right triangle that corresponds to the angle.

Let's convert the angle to degrees to more easily see the special right triangle that it creates.

Find the reference angle by subtracting the angle from from 180 degrees.

This means that 135 degrees is a 45 degree angle that lies in the second quadrant. Recall that the second quadrant contains positive values and negative values.

Therefore the special triangle that is created with is 45-45-90 degree triangle. The angle which is made at the origin will be 45 degrees and the length of the segment from the origin to the edge of the unit circle is one by definition.

Step 3: Calculate the side lengths of the special triangle.

From here, recall that the special 45-45-90 degree triangle has the following side identities.

Step 4: Calculate sine.

Recall the following trigonometric identities.

Since sine represents the values on the coordinate grid, this means that sine remains positive for angles in quadrant two.