To solve for the unknown leg \( y \) of the right triangle using the Pythagorean theorem, the correct equation is:
\[ 8^2 + y^2 = 12^2 \]
This means that the option that represents this equation is:
82 + y2 = 122
This option correctly applies the Pythagorean theorem, where \( a^2 + b^2 = c^2 \) (with \( a = 8 \) and \( c = 12 \)).