I was thinking the exact same thing by showing cos(45°) but it still doesn't prove it since we need to show if cos x is rational, then cos 3x is rational....then show cos 5° is irrat. based on the previous two proofs...?
I was thinking the exact same thing by showing cos(45°) but it still doesn't prove it since we need to show if cos x is rational, then cos 3x is rational....then show cos 5° is irrat. based on the previous two proofs...?
Yes it does.
If assume
Is rational and you arrived at a contradiction.
If is a rational number then, is a rational number.
Because when you add or multiply rationals you get a rational.