problem Spike of a Pyramide

[Gabry10]

hi guys, I'm still writing you because I have some trouble, actually very probably stupid but I swear I've been sneaking in all the ways but I can't get to top the edges of a pyramid.
then to clarify better this is the picture of the drawing
and I should cut those parts that go out that I highlighted by making lines inside.

I should do this design and the goal is the pyramid below
I tried obviously both with top edges, but it cuts me over the top of the pyramid, and with tip (also because of the lines to have a reference), but it cuts me only perpendicularly, and also changing the ucts I can not make him take the road I want.
Excuse me, but I'm freaking out.
Thank you very much in advance

edit: ah I forgot to say I use autocad 2013

 

[doking]

make the bird for three points and use the pull command

 

[GP.]

make the bird for three points and use the pull command

or better still draws with option "3p" :smile:

 

[Gabry10]

Hell it was so simple! Thank you very much, I finally chewed everything and I also discovered the command trancia 3p :d