11. In fig. 1, ∆ ABC is circumscribing a circle, the length of BC is _______ cm.
12. Given ∆ABC~∆PQR, if AB/PQ = 1/3, then ar(∆ ABC) / ar (∆PQR) = ________.
13. ABC is an equilateral triangle of side 2a, then the length of one of its altitude is _______.
14. (cos 80°/sin 10°) + cos 59° cosec 31° = _______.
15. The value of [sin²θ + 1/(1+tan²θ)] = ________.
OR
The value of (1+tan²θ)(1-sinθ)(1+sinθ) = _______.