Why does sin^2θ/cos^2θ-1 simplify to sin^θ/-sin^θ?

Aculture started with 3000 bacteria. after 5 hours it grew to 3900 bacteria. predict how many bacteria will be present after 9 hours

At a kentucky friend chicken, a survey showed 2/3 of all people preferred skinless chicken over the regular chicken. if 2,400 people responded to the survey, how many people preferred regular chicken?

Write the expression 7x^3-28xy^2 as the product of 3 factors