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Trigonometry: The Unit Circle (Part 2)

Sorry for not posting for such a long time. I have been busy with some schoolwork and i got sick.

This post is part of a series of posts on Trigonometry. To see all the posts, click on the tag #TrigonometryTutorials below. This is the post you should read before you read this.

Last time we talked about the new Definitions of the trig functions now that we know the unit circle.

\(\sin \theta\) is the \(y\) co-ordinate reading of the unit circle, \(\cos \theta\) is the \(x\) co-ordinate reading of the unit circle, and \(\tan \theta\) is the \(y\) divided by \(x\)

When you learnt co-ordinate geometry you learnt about quadrants

In Q I both \(x\) and \(y\) are positive, so sine, cosine, and tangent are all positive when \(\theta\) is in QI.

In QII \(x\) is negative but \(y\) is positive, so in QII only sine is positive, and Cosine and Tangent are negative

In QIII both \(x\) and \(y\) are negative. Only Tangent is Positive as tangent is \(y\) divided by \(x\) the negatives are cancelled. Sine and Cosine are Negative in QIII

In QIV \(y\) is negative but \(x\) is positive, so in QIV only cosine is positive, and Sine and Tangent are negative

Note by Yan Yau Cheng
3 years, 8 months ago

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Keep on posting. Sharky Kesa · 3 years, 8 months ago

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