/sci/ - Science & Math

I haven't really had much experience with proofs, can anyone help me get started on this? I'm pretty sure I understand what's going on, like if you factor out constant in a function you'll still get the same answer when you plug in numbers, and then multiply by the constant at the end.

I can prove that numerically by factoring out the constants(or constant if I need to find the common denominator), and plugging in values for x1, x2, and x3, but I don't know if there's another way I should go about it. This is similar to a homework question I have, I made this one up just to get an example of how I should go about this.

Probably super brainlet question, plz no bully