Right-angled triangles have special rules that let you find missing sides and angles. This unit covers Pythagoras' theorem and the basic trigonometric ratios.
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The right-angled triangle
A right-angled triangle has one angle of exactly 90 degrees.
The hypotenuse is the longest side and is always opposite the right angle.
The opposite side is across from the angle you are working with.
The adjacent side is next to that angle, but is not the hypotenuse.
Check you've got it
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1. In a right-angled triangle the two shorter sides are 3 and 4. What is the length of the hypotenuse?
2. Which of these is Pythagoras' theorem?
3. According to SOH, the sine of an angle equals what?
4. In a right-angled triangle, the hypotenuse is which side?
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