Find the missing length of the triangle

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

A33 gram sample of a substance that's used to detect explosives has a k-value of 0.1473. n = noekt no = initial mass (at time t = 0) n = mass at time t k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days

If the scale factor between two circles is 2x/5y what is the ratio of their areas?