How to recipacte fractions

What basic trigonometric identity would you use to verify that sin x cos x tan x =1-cos^(2)x?

Brian, chris, and damien took a math test that had 20 questions. the number of questions brian got right is 14 more than the number of questions chris got right. damien correctly answered 2 less than the number of questions chris answered correctly. if brian and damien have the same score, which statement is true?

In triangle △abc, ∠abc=90°, bh is an altitude. find the missing lengths. ah=4 and hc=1, find bh.