What is useful in checking a quotient for long division.

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?

What is x3+3x2−16x−48 divided by x−1?