The value of tan π16+2tanπ8+4 is equal to
Using tanA=cotA–2cot2A
we have LHS
(cot2A=cot2A−12cotA)
=(cotπ16−2cot2π16)+2(cotπ8−4cotπ4)+4cotπ16−2cotπ8+2cotπ8−4cotπ4+4
=cotπ16−4+4(ascotπ/4=1)
=cotπ16