First lets try drawing it by hand!

1. Go 'Co-N' for a new image window, something like 200ppi resolution, and 1000 pixels square.
Select your BrushTool (B) and choose a colour by clicking the colour swatch in the Tool Bar.
To change the size of the brush (Co - { to reduce the size, or Co - } to increase).


Now start drawing the triangle, starting and ending at bottom left. .....mmmmm, not easy is it,
and it's not straight by any stretch of the imagination is it! So lets try another way.

2. Select Black and White 'D' in the tool bar colour swatch, then press the 'X' key to bring
white to the top. Then fill 'Alt/Option-Backspace/Delete' the rectangle with white
so we have a clean slate. We will now put some guides in place first in order to define the
size of our proposed triangle.

3. Go to 'View - New Guide' then choose Vertical, and type in 50%.



This gives you a blue guide down the centre of your image. Now we need to set left and
right guides.
4. Do the same as the above and lets say10% for the left, and 90% for the right.

5. Next, go 'Co-R' to get your Rulers, then drag with your Move Tool to get a horizontal line.
Just drag this from the Ruller bar, to somewhere near the lower half of your image.




You should now have this on your page. Okay now lets draw this thing.

6. Choose your Brush Tool (B) and make a starting point by clicking in the lower left corner like so ...


Then keep your 'Shift key' held down and click but don't draw the apex of the triange (to determine
the top) then the lower right, finally back to the lower left. Every time you click with Shift held down,
Photoshop draws a straight line between the clicks or points you made. And that's it.




This method can be applied to most drawing tools, even the Clone Stamp tool as well.
Have fun!
Jon