Quick Pendulum and Trig Question

[seuzy13]

Homework Statement

This is taken from a much larger problem, but I only need the answer to one particular question. Please help me understand why the height that a pendulum swings is r(1-cos$$\theta$$) where r is the length of the string and theta is the angle it swings through.

Homework Equations

h = r(1-cos$$\theta$$)

The Attempt at a Solution

I'm afraid trigonometry's one of my weakness. I can't begin to understand why this is the case. I'm sure it involves a crazy mess of right triangles.

 

[rock.freak667]

If you draw a vertical line to represent the pendulum at initial position and then draw it at a general angle, if you draw a horizontal line from the bob to meet the vertical line, you will get a right angled triangle.

In the right angled triangle, the hypotenuse is 'r'.

So what is the adjacent side of this triangle in terms of 'r' and the angle? (Hint: use cosine)

 

[seuzy13]

Ah, okay. I see now. Thank you!