Question

Prove that tan 10°,tan 15°,tan 75°,tan 80°= 1

Answer 1

tan10.tan15.tan75.tan80=1
tan(90-80).tan(90+-75).tan75.tan80=1
cot80.cot75.tan75.tan80=1
1/tan80.1/tan75.tan75.tan80=1
1=1
LHS=RHS
hence proved

Answer 2

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