Usually in proofing, you're not allowed to substitute numerical value. Maybe this will do :
If , then :
The question is,
Let K be a scalar and let U = (Ux,Uy,Uz). Prove that ||kU|| = |k| ||U||
I'm not entirely sure what the question is asking here, I'm getting confused with the meaning of the bars ||kU|| and |k| and ||U||.
I'd think ||kU|| would be U = (k * Ux, k* Uy, k * Uz).
Would it be better to prove this scenario by assigning the variables values, like let k = 6, U = (-5, 4, 8). So ||6U|| = (6 * -5, 6 * 4, 6 * 8).
I think my problem might be stemming from not understanding the question or I might just be losing the plot.