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# c3 trig watch

1. Could somebody explain how to deal with the fact the angle is 270<x<360.

I understand how to do this if the angle is 0<x<90

when it should be
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2. It has to be negative. When you draw a sinx graph, 270<x<360 will always give you a negative value
3. It means that sinA = -sqrt(1-cos^2(A)). If you think about the unit circle, 270 < x < 360 is the 4th quadrant. In this quadrant, y < 0, so sinx < 0. So when we apply Pythagoras' identity to cosA to find sinA, we need to take the negative because sinA < 0.
4. (Original post by Unnamed User)
It has to be negative. When you draw a sinx graph, 270<x<360 will always give you a negative value
(Original post by Desmos)
It means that sinA = -sqrt(1-cos^2(A)). If you think about the unit circle, 270 < x < 360 is the 3rd quadrant. In this quadrant, y < 0, so sinx < 0. So when we apply Pythagoras' identity to cosA to find sinA, we need to take the negative because sinA < 0.
of course, thanks a lot !

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