Answer 1

tan 35° = tan (90° - 55°) = cot 55°

tan 40° = tan (90° - 50°) = cot 55°

tan 65° = 1

cot 55 tan 55∙ cot 50 tan 50 ∙ tan 45

1 ∙ 1 ∙ 1 = 1