Math  /  Trigonometry

QuestionFind the reference angle. A) 11π36\frac{11 \pi}{36} B) π9\frac{\pi}{9} C) 5π18\frac{5 \pi}{18} D) 2π9\frac{2 \pi}{9}

Studdy Solution

STEP 1

What is this asking? We need to find the smallest angle between the terminal side of 41π18 \frac{41\pi}{18} and the x-axis. Watch out! Reference angles are always positive and less than or equal to π2 \frac{\pi}{2} .

STEP 2

1. Revolutions
2. Find the coterminal angle
3. Determine the quadrant and calculate the reference angle

STEP 3

Let's **rewrite** our angle 41π18 \frac{41\pi}{18} in terms of full revolutions (2π 2\pi ).
We can think of 41π18 \frac{41\pi}{18} as a mixed number of revolutions!

STEP 4

We **divide** 4118 \frac{41}{18} to get 2 2 with a remainder of 5 5 .
So, 41π18 \frac{41\pi}{18} is the same as 2π+5π18 2\pi + \frac{5\pi}{18} .
This means we have **two full revolutions** and an extra 5π18 \frac{5\pi}{18} radians!

STEP 5

Coterminal angles are angles that share the same terminal side.
Since 41π18 \frac{41\pi}{18} is the same as two full revolutions plus 5π18 \frac{5\pi}{18} , the **coterminal angle** we're interested in is just 5π18 \frac{5\pi}{18} .

STEP 6

Since 5π18 \frac{5\pi}{18} is between 0 0 and π2 \frac{\pi}{2} (which is 9π18 \frac{9\pi}{18} ), our angle is in the **first quadrant**!

STEP 7

For angles in the first quadrant, the reference angle is simply the angle itself.
Therefore, the **reference angle** is 5π18 \frac{5\pi}{18} .

STEP 8

The reference angle for 41π18 \frac{41\pi}{18} is 5π18 \frac{5\pi}{18} , which is option C!

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