Question

prove that tan tan10 yan 20 tan 70 tan80 tan 89=1

Answer 1

Use the property tan(90 - x) = cot(x). Hope this is helpful.

Answer 2

tan1 tan(90-80) tan20 tan(90-20)tan80
tan(90-1).
tan1 cot80 tan20 cot20 tan80 cot1.
tan1 cot1 tan80 cot80 tan20 cot20.
$1 \times 1 \times 1$
=1