What is ac? i need help

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

Abag contains 4 red, 7 blue and 5 yellow marbles. event a is defined as drawing a yellow marble on the first draw and event b is defined as drawing a blue marble on the second draw. if two marbles are drawn from the bag, one after the other and not replaced, what is p(b|a) expressed in simplest form? a. 7/16 b. 7/15 c. 14/16 d. 14/15

∆red ≅ ∆ by rule will give brainiest if possible