Question

I need help with this please​

Answer 1

use the pythagorean theorem:
a^2 + b^2 = c^2

a & b are the sides, while c is the hypotenuse (the side opposite from the 90° angle).

so, plug in the numbers:
12^2 + y^2 = 13^2
144 + y^2 = 169
y^2 = 25
y = 5

the missing side is equal to 5