Please help me solve this

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

Which of the following is the missing term, a2, of the geometric sequence in which a1=2 and a3=200

Some boys and girls were asked if they had a pet. one third of the group were boys. there were 20 boys. 20% of the girls had a pet. boys with a pet : girls with a pet = 1 : 5 i need to know how many girls there are.