Question

cần gấp

 

Answer 1

B = 1 - sin²30⁰ - sin²60⁰ + tan²50⁰(1 - 1/cos²40⁰)

= 1 - (sin²30⁰ + sin²60⁰) + tan²50⁰.(-tan²40⁰)

= 1 - (sin²30⁰ + cos²30⁰) - tan²50⁰.cot²50⁰

= 1 - 1 - 1²

= -1