Dear student
I think there should not be any positive sign.
If it contains multiply sign between each term..then,
Tan 10 * tan 20 * tan30 * tan40 * tan 50 * tan 60 * tan70 * tan80
tan 10 * tan 20 * tan30 * tan 40 * tan(90-40) * tan (90-30) * tan (90-20)* tan (90-10)
tan 10 * tan 20 * tan 30 * tan 40 * cot 40 * cot 30* cot 20 * cot 10
Hence all canceks out and
Answer is 1.
Regards
Arun (askIITians forum expert)