Gievn that tan x = cot(x) - 2cot(2x),

Show that 2tan20 + 4tan40 + 8tan80 = 9(cot10 - tan10)

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- Jan 9th 2010, 06:32 AMPunchSubstitution? Confused!
Gievn that tan x = cot(x) - 2cot(2x),

Show that 2tan20 + 4tan40 + 8tan80 = 9(cot10 - tan10) - Jan 9th 2010, 06:43 AMProve It
- Jan 9th 2010, 05:28 PMPunch
why do i have to change to , is it possible work with the tan120 below?

if it's not possible, then may i would like to ask if it is true that i have to change all the angles to acute? - Jan 9th 2010, 06:31 PMProve It
- Jan 10th 2010, 07:26 AMGrandad
Hello everyone

A slight variation at the end:

Once you get to , use the original result, re-arranged as: