I need help with a science fair project.

I will tell u briefly what i am trying to do. In a Science Fair, i need to prove
that sound, radio, and light waves can be affected by destructive interference.
I already have used my computer to lower the dB of a given sound wave by about
85%. I have taken one speaker from the computer and angled it about 10 degrees
toward the other, and let one speaker play the opposite continuous tone as the
other (at 350Hz). This works fine. Radio and light waves are much more difficult to do a demonstration for, so i hope that i can JUST prove the possibility of canceling them out using just math. I read that light waves are known to spike randomly quite a bit, so it will be difficult in a real life situation to use a computer to cancel them. I also wanted to suggest to people that this may be practical when used as a shield or dampening field for radiation.

My question is, can someone help me prove mathematically that destructive interference works with radio waves and light waves? need some actual equations form u guys

and does anyone have any suggestions to make the project more interesting to judges

thank you for your time everyone