This is a proof that the angles in a triangle equal 180°:
The top
line (that touches the top of the triangle) is
running parallel
to the base of the triangle.
So:
<span> <span>angles A are the same </span> <span>angles B are the same </span> </span>
And you can easily see that A + C + B does a complete rotation from one side of the straight line to the other, or <span>180°</span>
