What is the domain of f(x) = 5x – 7

This is a line function. 
You can put any real number for x, and you get a real number for y.

Domain of a line function is all real numbers.

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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.