To find the length of the diagonal of a rectangular prism, you can use the formula:
\[ d = \sqrt{l^2 + w^2 + h^2} \]
where:
- \( d \) is the length of the diagonal,
- \( l \) is the length,
- \( w \) is the width,
- \( h \) is the height.
Given:
- \( l = 3 \)
- \( w = 4 \)
- \( h = 12 \)
Now plug in the values:
\[ d = \sqrt{3^2 + 4^2 + 12^2} \] \[ d = \sqrt{9 + 16 + 144} \] \[ d = \sqrt{169} \] \[ d = 13 \]
Thus, the length of the diagonal of the prism is \( 13 \) units.