Jika 2 cos (x+1/4 phi) = cos (x-1/4 phi) buktikan bahwa tan x = 1/3

2 cos (x+45)=cos (x-45)
2(cos x cos 45 - sin x sin 45)= cos x cos 45 + sin x sin 45
2(½√2 cos x - ½√2 sin x) = ½√2 cos x + ½√2 sin x
√2 cos x - √2 sin x=½√2 cos x + ½√2 sin x
-√2 sin x - ½√2 sin x=½√2 cos x - √2 cos x
-3/2√2 sin x=-½√2 cos x
sin x / cos x=-½√2 / -3/2√2
Tan x=-½√2. (-2/3√2)
=2√2 / 6√2
=⅓