# G20b – Trigonometric ratios – sin, cos and tan

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Prerequisites
Desirable but not essential:

# Similar triangles and ratios – sin, cos and tan

In the right-angled triangle below, the green side is called the hypotenuse.

For the reference angle given in blue, the blue side is called the opposite side.

The red side is called the adjacent side.

Pick an angle and stick with it.

Work out the value of $$\dfrac{\color{Blue}{opposite}}{\color{Green}{hypotenuse}}$$ as you change the size of the triangle. What do you notice?

Work out the value of $$\dfrac{\color{Red}{adjacent}}{\color{Green}{hypotenuse}}$$ as you change the size of the triangle. What do you notice?

Work out the value of $$\dfrac{\color{Blue}{opposite}}{\color{Red}{adjacent}}$$ as you change the size of the triangle. What do you notice?

# Trigonometric ratios – sin, cos and tan

Teacher resources

• Slides in PPTX
• Slides in PDF (one slide per page, suitable for importing into IWB software)
• Worksheet (with space for student work)
• Handout (slides with exercises only; 4 per page for reduced printing)
• Card sort – choosing whether to use sin, cos or tan