Jika x sudut lancip tan x= 5/akar 11, maka tan 2x=

tan2x = 2tanx/(1 - tan^2 x)
tan2x = 2×(5/akar11) / (1 - (5/akar11)^2)
tan2x = 10/akar11 / (1 - 25/11)
tan2x = 10/akar11 / ((11-25)/11)
tan2x = 10/akar11 / (-14/11)
tan2x = 10×11/(akar11×(-14)
tan2x = 5akar11 / (-7)
tan2x = -5/7 akar11