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(I'm new and only have 1 reputation. Please be very nice with me.) Hello guys, I'm just wondering, What is a sine chart in math? I've heard about these in a question and in my mind I was like "What in the world is a sine/sign chart?". Can you please help me out? Thank you to all who tries to help out. I would really appreciate it.

Ricardito10
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I think you mean a sign chart, rather than a sine chart. Sine is the name of a specific function.

So, what we mean by a sign chart is a chart that tells us where a function $f(x)$ is positive or negative.

For example, consider $f(x) = (x - 2)(x - 3)$. This is a function. To create a sign chart, we first find the $x$ values that make this function $0$. That would be $x = 2$ and $x = 3$.

We mark those on a number line. Then, for every region on the number line, we plug a test point from that region into the function, and figure out if the output number will be positive or negative. If it is positive, then the function $f(x)$ is positive on that entire region where the test point came from. If the output is negative, then the function $f(x)$ is negative on the entire region where the test point came from.

layman
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    For an example of what a sign chart looks like, see the answer at this question: http://math.stackexchange.com/questions/181786/how-does-one-construct-a-sign-chart-when-solving-inequalities – layman Nov 26 '15 at 18:02
  • Oh. I heard of it as a sine chart. Thanks for helping me! – Ricardito10 Nov 26 '15 at 18:03
  • @Ricardito10 If you have seen it spelled sine chart, then could they possibly mean the actual plot/graph of the $\sin(x)$ function? – layman Nov 26 '15 at 18:04
  • Umm... maybe. I was confused between the difference of that and the sign chart. Once again thanks for helping me. Nice reputation you got there (9,024 reputation?! Wow! Nice job!). – Ricardito10 Nov 26 '15 at 18:05
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    @Ricardito10 Well, $\sin(x)$ is a specific function. Try typing "sin(x)" into google images and see what it looks like. – layman Nov 26 '15 at 18:17
  • @Ricardito10 You're welcome! :) – layman Nov 26 '15 at 18:21
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If you are referring to the trig functions sine/cosine .. they could be graphs of projections of a point going round a point on a diameter or its perpendicular of circle described.

Narasimham
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