Jack broke apart 5 times 216 as ( 5 times 200) + ( 5 times 16) to multiply mentally. what strategy did he use

He used a method called foil . 

Hello! i hope this
since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.