How do I find my angle using sin and cos values?

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In summary, to find the angle from given values of sin(angle) and cos(angle), you can use inverse sin and cos functions. However, if the angle is not between 0 and 360, you can use either of two methods - using graphs or a unit circle. By looking at the signs of sin(angle) and cos(angle), you can determine the quadrant the angle is in and use inverse functions to find the angle. In the given example, the angle was found to be 200 degrees by using inverse sine and cosine functions.
  • #1
Ascending One
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So, I have the values for sin (angle) and cos (angle)... how do I get back to my angle?
 
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  • #2
Use the inverse sin and cos functions.
 
  • #3
But say my angle is 200. So I have inverse cosine(cosine (200)) which equals... 160. That's not what I want.
 
  • #4
You can do either of two things:
1) Use, if only in your head, graphs for y= sin(x) and y= cos(x), draw horizontal lines at the value of sin(x) on the first and cos(x) on the second.

2) (And I think this is what you really want since I suspect you are requiring the angle be between 0 and 360) draw, again if only your head, a "unit circle" (circle on a coordinate system with center at (0,0) and radius 1) and remember that (cos(t),sin(t)) are the coordinates of the point at angle t, counter-clockwise around the circle from the positive x-axis. You can distinguish between the various values by looking at signs.
For your example, where sin(t)= -.3402 and cos(t)= -.9397, since both are negative, you are in the 3rd quadrant. You know immediately that t is between 180 and 270 degrees. Using "inverse sine", or arcsin, of -.3402 on a calculator (have made sure it is set to "degree mode"!) you get -20 degrees which is in the fourth quadrant. The corresponding angle in the third quadrant (20 degrees below the x-axis just as -20 is) is 180+ 20= 200 degrees. If I had used inverse cosine of -.9397, would have gotten 160 degrees, in the 2nd quadrant, 180- 160= 20 degrees above the x-axis. Knowing the the angle I want is in the 4th quadrant, I know it must be 20 degrees below the x-axis: 180+ 20= 200 degrees, again.
 
  • #5
I used your method. Thank you!
 

FAQ: How do I find my angle using sin and cos values?

1. How do I measure angles?

To measure an angle, you can use a protractor or a measuring tool with a degree scale. Place the center of the protractor on the vertex of the angle and align one of the sides of the angle with the baseline on the protractor. Read the degree measure where the other side of the angle intersects with the scale.

2. What is the unit of measurement for angles?

The most common unit of measurement for angles is degrees, denoted by the symbol °. A full circle is 360°, and angles can be measured in degrees from 0° to 360°.

3. How do I find the measure of an unknown angle?

If you know the measures of the other angles in a figure, you can use the angle sum property to find the measure of the unknown angle. For example, in a triangle, the sum of all angles is 180°. So, if you know the measures of two angles, you can subtract their sum from 180° to find the measure of the third angle.

4. Can angles be negative?

Angles are typically measured in a counterclockwise direction, starting from the positive x-axis. In this case, angles are never negative. However, if you are measuring angles in a clockwise direction, they can be negative. Generally, it is best to measure angles in the positive direction.

5. How do I find the measure of an angle using trigonometry?

You can use trigonometric functions like sine, cosine, and tangent to find the measure of an angle in a right triangle. For example, if you know the lengths of two sides of a right triangle, you can use the inverse tangent function to find the measure of the angle opposite the known sides.

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