Question 875836
If it's an isoceles right triangle then it means that the The perpendicular and the base side are equal in length and let's suppose them to be 'x'.

So using the Pythagoras Theorem:
x^2 + x^2 = 12^2
4x^2 = 144
x^2 = 144/4 = 36
&#8730;x = &#8730;36 = 6