Why Is Cosine Used Instead of Sine in Calculating Tension in Physics?

[-EquinoX-]

Homework Statement

Here's the picture and I am asked to calculate the tension in the tie rope between the rod and wall

http://img399.imageshack.us/img399/2625/masslg8.jpg
http://g.imageshack.us/img399/masslg8.jpg/1/

Homework Equations

The Attempt at a Solution

The answer key is:

http://img399.imageshack.us/img399/4733/answermo0.jpg
http://g.imageshack.us/img399/answermo0.jpg/1/

I just want to know why is it using cos 60 instead of sin 60?

 

[needlottahelp]

because the angle created by the rope holding the block and the slanted thinger is 30 degrees (right triangles). So instead of putting sin 30 they just put cos 60 because sin 30 = cos 60. i hope you understand what I'm talking about