Finding angle of a reflected isosceles triangle

In summary, the given problem involves finding an angle marked in red, which is formed by the radii of two circles and the horizontal line. The text states that this angle is 2θ, but the attempt at a solution using symmetry yields an angle of π-2θ. By considering the geometry of the figure, it can be determined that the angle in question is actually the bottom angle of a diamond shape formed by the apex of a blue triangle and the inverted triangle. This angle is equivalent to the sum of the left and right angles in the diamond, which are known to be θ based on the given information. Therefore, the desired angle is 2θ.
  • #1
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Homework Statement


I am trying to find the following (marked in red) angle, I know that the radii to the points of contact make an angle θ with the horizontal.

2me5pw0.jpg



Homework Equations


all angles of a triangle add up to 180 degrees.
isosceles triangle, has two equivalent sides


The Attempt at a Solution


5l0yv8.png


I tried using symmetry and found the part in red is [itex]\pi[/itex] - 2[itex]\theta[/itex]
but according to the text, the angle is 2[itex]\theta[/itex]. I am confused on why is is 2[itex]\theta[/itex]
 
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  • #2
The sides of the inverted triangle are tangents to each circle.
The base of your blue triangle is 2R.
The angles on either side of the base must be ##\theta##.

The blue-triangle apex angle must be ##\pi-2\theta## ... which is where you've got up to.

The apex of the blue triangle forms a diamond shape with the inverted triangle.
The bottom of the diamond is the angle you want.
The left-hand angle is the same as the right-hand angle - you actually know what these angles are!

What do the angles in the diamond add up to?
What do the left hand and right hand angles add up to?
 

1. How do you find the angle of a reflected isosceles triangle?

The angle of a reflected isosceles triangle can be found by using the law of reflection, which states that the angle of incidence is equal to the angle of reflection. In this case, the angle of incidence is the angle formed between the incoming ray and the normal line, and the angle of reflection is the angle formed between the outgoing ray and the normal line.

2. What is the normal line of a reflected isosceles triangle?

The normal line of a reflected isosceles triangle is an imaginary line perpendicular to the surface of the reflecting object. It is used to determine the angle of incidence and the angle of reflection.

3. Can the angle of a reflected isosceles triangle be greater than 90 degrees?

No, the angle of reflection cannot be greater than 90 degrees. This is because the law of reflection states that the angle of incidence and the angle of reflection must be equal.

4. How does the angle of a reflected isosceles triangle change if the reflecting surface is curved?

If the reflecting surface is curved, the angle of reflection will vary depending on the curvature of the surface. However, the law of reflection still applies, meaning that the angle of incidence will always be equal to the angle of reflection.

5. Can the angle of a reflected isosceles triangle be negative?

No, the angle of reflection cannot be negative. The angle of reflection is always measured as the angle between the outgoing ray and the normal line, and angles are typically measured in a counterclockwise direction from the positive x-axis. Therefore, the angle of reflection will always be a positive value.

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