5.9 Chapter summary
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5.8 Defining ratios in the Cartesian plane

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5.9 Chapter summary (EMA3Y)

We can define three trigonometric ratios for rightangled triangles: sine (\(\sin\)), cosine (\(\cos\)) and tangent (\(\tan\))
These ratios can be defined as:
 \(\sin \theta = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{y}{r}\)
 \(\cos \theta = \frac{\text{adjacent}}{\text{hypotenuse}} = \frac{x}{r}\)
 \(\tan \theta = \frac{\text{opposite}}{\text{adjacent}} = \frac{y}{x}\)

Each of these ratios have a reciprocal: cosecant (\(\text{cosec }\)), secant (\(\sec\)) and cotangent (\(\cot\)).
These ratios can be defined as:
 \(\text{cosec } \theta = \frac{\text{hypotenuse}}{\text{opposite}} = \frac{r}{y}\)
 \(\sec \theta = \frac{\text{hypotenuse}}{\text{adjacent}} = \frac{r}{x}\)
 \(\cot \theta = \frac{\text{adjacent}}{\text{opposite}} = \frac{x}{y}\)

We can use the principles of solving equations and the trigonometric ratios to help us solve simple trigonometric equations.

For some special angles (0°, 30°, 45°, 60° and 90°), we can easily find the values of \(\sin\), \(\cos\) and \(\tan\) without using a calculator.

We can extend the definitions of the trigonometric ratios to any angle.
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