Here, triangle ABC is a right triangle with AB = AC. It mens its a 45-45-90 special triangle .
So we need to use the formula that determines the relationship between legs and hypotenuse and the formula is
[tex] Hypotenuse = leg * \sqrt 2 [/tex]
In the given diagram, leg = 12, so hypotenuse AC
[tex] AC = 12 \sqrt 2 [/tex]
