Find the greatest common factor of 21, 24, 27

What are the solutions of the equation? 16x^2 + 24x + 5 = 5 a. 1/4, 5/4 b. -1/4, -5/4 c. -1/4, 5/4 d. 1/4 , -5/4

Acompany that manufactures and sells guitars made changes in their product range. from the start they had 20 models. then they reduced the number of models to 15. as a result, the company enjoyed a 10% increase in turnover. - how much did the stock level change? in (%)

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.