Answer question 3a

Dear Student,

tan20° tan35° tan55° tan70°
= tan (90-70)° tan (90-35)° tan 35° tan 70°
= cot70° cot35° tan35° tan 70°
= cot70° cot 35° (1/cot35°) (1/cot70°)
= 1
Hence, proved.

Regards
​​​​​​