Evaluate the following algebraic expression by substituting. x-y; where x=25 and x=20
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According to modern science, earth is about 4.5 billion years old and written human history extends back about 10,000 years. suppose the entire history of earth is represented with a 10-meter-long timeline, with the birth of earth on one end and today at the other end.

How can you tell when x and y are not directly proportional?

If sin(x) = 0 and cos(x) = 1, what is tan(x)?