How can i draw symmetric triangles

I hope that i understood the question right.
I will tell you how to draw symmetric triangles in solidwork.
first draw half your sketch in sketch item. here you should draw half of your triangle.
then use center line to mirror your drawing. after that you have to select all you drawn contains lines and center lines. at last click on Mirror Entities.
Its done. you already have want you want.
I upload a pic and you can use it.

I don't fully understand the question either, but I have two other ideas:
1. You can save a triangle you've drawn as a Block. You can then reuse this block multiple times.
2. Instead of using a Block, you can use a Derived Sketch.

Which method you use really depends on what the goal is.
If you post some pictures of what you are trying to do, I'm sure there are some better options.

(I thought I saw a picture attached to the original question that helped describe the situation)

I have a different method for this, that I explained with a tutorial: Triangles? Draw the cross members instead.

Here's pics and a model to go with what Jack Knapp suggests, and using a "rib" feature to create the members in one shot. (I realize it doesn't look quite like your original picture, but it serves as an example)

Rib features have some particular requirements to work, so there will be a step after their creation to cut away the wall needed for the ribs to project to.

The sheet metal aeration function can also work and simplify the work. It allows a single sketch to pierce a window in a sheet at the same time as to add amounts and reinforcements. Variations are then possible and the sketch is not limited to rectilinear segments.