cos (x-30)=sin x tunjukkan bahwa tan x=√3

cos (x-30)=sin x
(cos x cos 30 + sinx sin 30) = sin x
cosx . 1/2 √ 3 + sin x . 1/2 =sin x
sama2 kali 1/ cos x setiap ruas

(1/cos x .cosx) . 1/2 √ 3 +1/cosx . sin x . 1/2
=(1/cos x. sin x)

1/2 √ 3 +tan x . 1/2 =tan x
1/2 √ 3 =tan x - 1/2 tan x
1/2 √ 3 = 1/2 tan x
(1/2 √ 3 ) : 1/2 =tan x
√ 3 =tan x ( terbukti)