Răspuns:
sin^2 a + cos^2 a=1=>sin^2 a=1-cos^2 a=>sin^2 a=1-16/25
sin^2 a= 9/25=> sin a= 3/5
tg a = sin a/ cos a => tg a= 3/4
ctg a= cos a/ sin a=> ctg a= 4/3
