What is 9 × 1/4 I do not know how to do it so can any one plz help me know how to do this Thank you

Express the following as a function of a single angle, cos(60) cos(-20) - sin(60) sin(-20)

Afruit stand has to decide what to charge for their produce. they need $10 for 4 apples and 4 oranges. they also need $15 for 6 apples and 6 oranges. we put this information into a system of linear equations. can we find a unique price for an apple and an orange?

Does the point (1, sqrt 7) lie on circle shown.