With finding the area and perimeter

Using the Pythagorean theorem, 12^2 + 12^2 = 288 (equal lengths of a right-angle triangle). the square root of 288 is 16.9 (could be rounded to 17).

Rounding up to 17, the perimeter (P) would be 41. Without rounding, it would be 40.9. 

Using the 17 measurement as the Base, the height would come out to 4.82. This can be used to find the Area, which comes out to being 41. 

If you would like to double check, the measurements based on the picture are: 
Sides: 12, 12, 17 
Angles: 45, 45, 90

I hope this helps!