im in 10th std cbse.how to solve trigonometry identities?i mean if i see the question how to come to know which identitiy shoud i use.??

Your question is not clear..

u guys are learning only 3 identities..

think  and apply the correct identity

sums that contain tan and sec, use sec²A - tan²A = 1

or some how convert other trigo ratios to suit to this identity and do the same for the other identities..

identity sums in the tenth are very easy.. once understood, its definately full-scoring.

All The Best.