Question

Evaluate cosec39°.cos51°+tan21°.cot69°-sec²21°

Answer 1

cosec(90-51) * cos51 +tan21*cot(90-21) -sec^2 21

sec51 * cos51 + tan21 * tan21 - sec^2 21

as we know that sectheta = 1/costheta 

then,

1+tan^2 21 - sec^2 21

tan^2 21 +1-sec^2 21

as we know that 1 + tan^2  theta = sec^2  theta 

then

sec^2 21 - sec^2 21


= 0 


i hope this will help you 




- by ABHAY