# Math Help - Find the angle in a Tetrahedron

1. ## Find the angle in a Tetrahedron

The point $P$ is the midpoint of the altitude of the regular Tetrahedron. $P$ is linked with $A , B$ of the base of Tetrahedron with segments $PA$ and $PB$.
Find the angles between these segments.

2. We say tha size of each one triangule is $l$, now $AC=CF=CB$ hence $
CB = \frac{{l\sqrt 3 }}
{3} \Rightarrow DC = \frac{{l\sqrt 6 }}
{3} \Rightarrow PC = \frac{{l\sqrt 6 }}
{6}
$

for other size

$
PC^2 + CB^2 = PB^2 \Rightarrow PB = \frac{{\sqrt 2 l}}
{2}
$

but: $
\sin \alpha = \frac{{GB}}
{{PB}} = \frac{{\frac{l}
{2}}}
{{\frac{{\sqrt 2 l}}
{2}}} = \frac{{\sqrt 2 }}
{2} \Rightarrow \alpha = \frac{\pi }
{4} \Leftrightarrow \measuredangle APB = \frac{\pi }
{2}
$

3. Originally Posted by Nacho

is this a regular tetrahedron ?
i thought that a regular tetrahedron is a regular 3 sides pyramid

4. Originally Posted by beq!x
is this a regular tetrahedron ?
i thought that a regular tetrahedron is a regular 3 sides pyramid
Tetrahedron - Wikipedia, the free encyclopedia