posted by Bill on .
Find the exact value of cos 300 degrees.
cos 300 = 1/2 = 0.500
how do you know? I am supposed to show my work.
You ought to know the rule on 30-60-90 triangles. If the hyp is 2, the shorter side is 1, and the longer side is sqrt3.
what does that have to do with cos300?
Cos(x) = Cos(-x) (1)
Cos(x + 360) = cos(x) (2)
Cos(300) = (using (2)) cos(-60) = (using (1)) cos(60) = using what Bobpursley wrote above 1/2
where did you get 60 from?
Bill, the sixty came from the addition formula above. 300 + 60 = 360
Bob, it says Cos(x + 360) .
Cos(x + 360) = Cos(x)
substitute x = y - 360:
Cos(y - 360 + 360) = Cos(y - 360) --->
Cos(y) = Cos(y - 360)
Substitute y = 300:
cos(300) = cos(-60)
Where did you get substitute x = y - 360 from? I'm sorry, I am so confused. Do you think you could give me the formula or whatever and then show me how to plug in the 300, or is that what you are doing now?